The question expects you to work it out using algebra even though it's easy to see that the triangles in the trapezium are congruent. From this I can see that 2/3 of the trapezium is shaded-but I can't seem to get this using algebra. here's what I tried:

Are of trapezium = 1/2(a+b)h

The area of the combined shaded triangles will be - 2[1/2(1/2bh)] =2(1/4bh) = 1/2bh. So the proportion will be:

(1/2bh)1/(2ah+1/2bh)

can't get this to equate to 2/3 ! Clearly something faulty I can't see (but will result in me slapping my forehead shouting out dooooh! when someone points it out.

Help appreciatively received.