This is a system of equation:
7y - 5x = 31
x = 4 - 2y
Plug in 4 - 2y for x
7y - 5(4 - 2y) = 31
Distribute -5 to both 4 and -2y
7y - 20 + 10y = 31
Simplify
17y - 20 = 31
Isolate the y. Note the equal sign. What you do to one side you do to the other. Do the opposite of PEMDAS.
Add 20 to both sides
17y - 20 (+20) = 31 (+20)
17y = 51
Divide 17 from both sides to isolate the y
17y/17 = 51/17
y = 51/17 or 3
y = 3
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Plug in 3 for y in one of the equations.
x=4−2y
x = 4 - 2(3)
Simplify.
x = 4 - 6
x = -2
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x = -2, y = 3 is your answer, or B)
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hope this helps
