I Cant write up my solution without LaTeX (markup language for mathematical text) and can't seem to find a way to use the whiteboard, so I shall try to explain my answer, and show my answer exactly if need be during the interview.
answer:re-write sin3x as sinxsin2x. Then using the identity of (sinx)^2+(cosx)^2=1, make the relevant substitution. I then expanded the brackets of the sinx. I then integrate sinx as normal and for the sinx(cosx)^2 I use the chain rule. I then evaluate the integral at the limits and obtain 2/3 as the answer.