Binomial Theorem or Binomial Coefficient

I hope this is the right part of the forum for this question.

In the expansion of (1+ax)^4, the coefficient of x^3 is 1372. Find the constant a.

Please Help !! (Crying)

So the coefficient of x^3 is

Can you solve this now?

By the binomial expansion, .

Solve for a.

Understand the pattern.

Thanks, i got it now, i had to equate the 4C3 part of the expansion to 1372x^3

Thanks