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d in (-oo:+oo)
2*(20-((1/4)*d)) = (3/10)*d+16 // - (3/10)*d+16
2*(20-((1/4)*d))-((3/10)*d)-16 = 0
2*((-1/4)*d+20)+(-3/10)*d-16 = 0
2*(20-1/4*d)+(-3*d)/10-16 = 0
(2*10*(20-1/4*d))/10+(-3*d)/10+(-16*10)/10 = 0
2*10*(20-1/4*d)-3*d-16*10 = 0
400-8*d-160 = 0
240-8*d = 0
(240-8*d)/10 = 0
(240-8*d)/10 = 0 // * 10
240-8*d = 0
240-8*d = 0 // - 240
-8*d = -240 // : -8
d = -240/(-8)
d = 30
d = 30
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