40659

We labelled the triangles A, B and C, before counting the cm in each one. Because the area of the square is 100cm,the number of cm in each triangle is the numerator of our fraction out of 100. This means that C would be 12.5/100,(1)A would be 25/100. Then we worked out B, we have to add C, A and another A( as there's two), and take it away from 100, which leaves 37.5/100. Then we needed to simplify the fractions. We did this by:
Working out how many times 25 went into 100. The answer was a quarter.

I then worked out C was 12.5cm (half of 25) so it had to be a eighth.

I then put the whole in to eighths, so B had to be 3/8.