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5*a = (36*x-(8*y))/21 // - (36*x-(8*y))/21
5*a-((36*x-(8*y))/21) = 0
5*a-((36*x-8*y)/21) = 0
(-1*(36*x-8*y))/21+5*a = 0
(-1*(36*x-8*y))/21+(5*21*a)/21 = 0
5*21*a-1*(36*x-8*y) = 0
105*a-36*x+8*y = 0
(105*a-36*x+8*y)/21 = 0
(105*a-36*x+8*y)/21 = 0 // * 21
105*a-36*x+8*y = 0
105*a-36*x+8*y = 0 // - 105*a+8*y
-36*x = -(105*a+8*y) // : -36
x = (-(105*a+8*y))/(-36)
x = (105*a+8*y)/36
x = (105*a+8*y)/36
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