Calculus: f(x) = log[base 3] (5x) ; Find the value of f'(2)

The answer should be 5/(5xln3)

I can't get to it though!

Let log[base 3] (5x) = Y

3^Y = 5X
Apply Ln for both sides
Ln ( 3^Y) = Ln (5X)
Differentiate both sides with respect to x
dy Ln3 = dx (1/5X) x 5

therefore
f(X) = 5/(5xln3)