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12-((4/5)*(x-15)) = 4 // - 4
12-((4/5)*(x-15))-4 = 0
(-4/5)*(x-15)-4+12 = 0
12-4/5*(x-15)-4 = 0
12-4/5*(x-15)-4 = 0
8-4/5*x+12 = 0
20-4/5*x = 0
20-4/5*x = 0
20-4/5*x = 0 // - 20
-4/5*x = -20 // : -4/5
x = -20/(-4/5)
x = 25
x = 25
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