The wording is a little confusing here, but the end goal is to find what fraction (written as P/Q) of the triangle is outside the two circles.

That is, our final answer should be (area of the region inside the triangle but outside the two circles) / (total area of the triangle).

Since the final answer is this fraction / ratio, you can actually pick convenient numbers for AB or AC, etc. and go from there.

Hope this helps!