Answer:
20) ![\displaystyle [4, 1]](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5B4%2C%201%5D)
19) ![\displaystyle [-5, 1]](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5B-5%2C%201%5D)
18) ![\displaystyle [3, 2]](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5B3%2C%202%5D)
17) ![\displaystyle [-2, 1]](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5B-2%2C%201%5D)
16) ![\displaystyle [7, 6]](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5B7%2C%206%5D)
15) ![\displaystyle [-3, 2]](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5B-3%2C%202%5D)
14) ![\displaystyle [-3, -2]](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5B-3%2C%20-2%5D)
13) 
12) ![\displaystyle [-4, -1]](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5B-4%2C%20-1%5D)
11) ![\displaystyle [7, -2]](https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5B7%2C%20-2%5D)
Step-by-step explanation:
20) {−2x - y = −9
{5x - 2y = 18
⅖[5x - 2y = 18]
{−2x - y = −9
{2x - ⅘y = 7⅕ >> New Equation
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
[Plug this back into both equations above to get the x-coordinate of 4]; 
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19) {−5x - 8y = 17
{2x - 7y = −17
−⅞[−5x - 8y = 17]
{4⅜x + 7y = −14⅞ >> New Equation
{2x - 7y = −17
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
[Plug this back into both equations above to get the y-coordinate of 1]; 
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18) {−2x + 6y = 6
{−7x + 8y = −5
−¾[−7x + 8y = −5]
{−2x + 6y = 6
{5¼x - 6y = 3¾ >> New Equation
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
[Plug this back into both equations above to get the y-coordinate of 2]; 
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17) {−3x - 4y = 2
{3x + 3y = −3
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
[Plug this back into both equations above to get the x-coordinate of −2]; 
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16) {2x + y = 20
{6x - 5y = 12
−⅓[6x - 5y = 12]
{2x + y = 20
{−2x + 1⅔y = −4 >> New Equation
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
[Plug this back into both equations above to get the x-coordinate of 7]; 
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15) {6x + 6y = −6
{5x + y = −13
−⅚[6x + 6y = −6]
{−5x - 5y = 5 >> New Equation
{5x + y = −13
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
[Plug this back into both equations above to get the x-coordinate of −3]; 
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14) {−3x + 3y = 3
{−5x + y = 13
−⅓[−3x + 3y = 3]
{x - y = −1 >> New Equation
{−5x + y = 13
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
[Plug this back into both equations above to get the y-coordinate of −2]; 
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13) {−3x + 3y = 4
{−x + y = 3
−⅓[−3x + 3y = 4]
{x - y = −1⅓ >> New Equation
{−x + y = 3
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
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12) {−3x - 8y = 20
{−5x + y = 19
⅛[−3x - 8y = 20]
{−⅜x - y = 2½ >> New Equation
{−5x + y = 19
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
[Plug this back into both equations above to get the y-coordinate of −1]; 
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11) {x + 3y = 1
{−3x - 3y = −15
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
[Plug this back into both equations above to get the y-coordinate of −2]; 
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