Prove that 9 is a factor of:

P(n): $\displaystyle 10^(^n^+^1^) + 3 * 10^n + 5$ for all positive integer n

Using the induction method,

I have proven P(1) to be true

P(k): $\displaystyle 10^k (10+3) + 5 = 9a$

P(k+1): $\displaystyle 10^(^k^+^1^) (10+3) + 5 = ?$

How do I continue? I am new at doing proofs