Two little questions relating to pi

I have just finished doing and marking a past paper. I did pretty well but there are two little 3-mark questions which I struggled with:

__Question 1__

Given that arcsinx = π/6, find x. Find arccosx in terms of π.

__Question 2__

The curve y = xsin3x crosses the x-axis at P. Find the x-coordinate of P.

According to the examiner's report both of these questions were meant to be simple but quite a few people couldn't understand them. So I would really appreciate if someone could explain in detail how to do each of these questions.

Much Thanx :)