Answer:
36
AE / AD = AB / AC
51 / 51 + 17 = x / x + 12
51 / 68 = x / x + 12
51 ( x + 12) = 68x (After cross multiplication)
51x + 612 = 68x
612 = 68x - 51x
612 = 17x
x = 612/17 = 36
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