The clue to this one was in the title! It uses the fact that if two triangles have the same height, then their areas are in the same ratio as their bases. So in this triangle, A/B=a/b.

Sim Jingwei, age 12, of Raffles Girls' Primary School, sent in this solution. She used x and y for the areas of the triangles indicated.

	Looking at the pair of triangles on either side of the blue line, they have the same bases, and so
Similarly with these four triangles,

Subtracting equation (2) from equation (1),
3y = 36
y = 12
2x = 8+12
x = 10
x+y = 22

So the required area is 22 square units.