This relies on knowing your special triangles, which include 30-60-90, 45-45-90, and 60-60-60.

If it helps, redraw the triangle so FG is at the bottom. For a 30-60-90, if the short side FG is 4, the hypoteneuse FH is 8. The radius would then be 4, and the area would be pi*r^2 or 16*pi.

If you forget the dimensions of 30-60-90 triangles, imagine doubling this triangle by reflecting FGH along the hypoteneuse FH. Then you would have an equilateral triangle, and each side would be 8.