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Find the coefficient of x3 in the binomial expansion of...

Find the coefficient of x3 in the binomial expansion of (3x+4)4 in ascending powers of x

A.

432

B.

194

C.

144

D.

108

Correct answer is A

(3x+4)4=4C0(3x)0(4)4+4C1(3x)1(4)3+4C2(3x)2(4)2+4C3(3x)3(4)1+4C4(3x)4(4)0

x3=4C3(3x)3(4)=4!3!1!×33×4

= 432x3