Determine the integral by making an appropriate substitution

integral of 8x cuberoot srqt(4x^2-9) dx

let u= 4x^2-9
du= 8x dx

I do not know what to do now

The substitution seems correct, but the question is not clear to me.

See response:
http://www.jiskha.com/display.cgi?id=1304200682