Evaluate the integral - Calculus Help

Integrate x * f(x^2) * dx when x = 0 to 3 and the integral of f(x) * dx = 4 from x = 0 to 9.
f is continuous.

I am not sure how to do this problem.

The trick is to perform a substitution: u = x^2. Then du = 2x dx and the integral becomes:

(1/2) ∫ u du, where the limits for u are from 0 to 9. This evaluates to exactly (1/2)(4) = 2. <== answer.