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(-4/5)*(x-15) = -4 // + 4
(-4/5)*(x-15)+4 = 0
4-4/5*(x-15) = 0
4-4/5*(x-15) = 0
16-4/5*x = 0
16-4/5*x = 0
16-4/5*x = 0 // - 16
-4/5*x = -16 // : -4/5
x = -16/(-4/5)
x = 20
x = 20
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