The Associative property of addition is where you group the numbers differently with parenthesis. That equation could be written as (8+6) + 7 = 21 or (7+8) + 6 = 21
All you have to do is regroup the numbers
I'd do this in reverse order. Mult. each of the 3 terms inside parentheses by 4:
8k^2 - 28k + 12
-2 (x-2y=-5)
-2x+4y=10
2x+3y=4
0+7y=14
/7. /7
y=2
2x+3 (2)=4
2x+6=4
-6. -6
2x=-2
/2. /2
x=-1
12x - 18 - 4x -2
12x - 4x = 8x (yours 12x - 4x = 8)
-18 - 2 = -20 (yours -18 -1 = 17)
answer:
8x - 20
