the series is 15k1 3xk I really need help with finding its i

the series is 1/(5^(k+1)) (3x)^k, I really need help with finding its integral, the 3 part near the end of the function is so confusing for me, any help would be much appreciated, thanks in advance!

If integral is to be found relative to x that is f(x)dx them k can be treated as constant( if not stated other wise)
so the function becomes
f(x)=1/[5^(k+1)*3^k *x^k]

now f(x)dx=[5^-(k+1)*3^-k*x^(-k+1) ]/-k