(4x - 20)/8 = 9y for x

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(4x - 20)/8 = 9y for x

Cross multiply:
4x - 20 = 8 * 9y
4x - 20 = 72y

Add 20 to each side to isolate x:
4x - 20 + 20 = 72y + 20

Cancel the 20 on the left side, we get:
4x = 72y + 20

Divide each side by 4:
4x/4 = (72y + 20)/4

Cancel the 4 on the left side:
x = (72y + 20)/4