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(3/4)*(16*x-4) = 21 // - 21
(3/4)*(16*x-4)-21 = 0
3/4*(16*x-4)-21 = 0
3/4*(16*x-4)-21 = 0
12*x-24 = 0
12*x-24 = 0
12*x-24 = 0 // + 24
12*x = 24 // : 12
x = 24/12
x = 2
x = 2
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