
### Instruction: help me answer this question Find a if the coefficients of x2 and x3 in the expansion of (3 + a x)9 are equal., think step by step
### Assistant: Coefficients of x2 and x3 in the expansion are equal if 9C2 * 3^7 * a = 9C3 * 3^6 * a , The answer is a = -12
