because if the perimeter of the rectangle is 28 then the length is 5, 5 - 11 = 6, the formula for finding the trapezium is to add the 2 parallel sides, half them, then times them with the length so your sum will look like this, 5+9=14, (i knew the other side was 9 as the length of AB is the same as the length of FC, which is the one of the parallel sides of the trapezium) then we do 14÷2=7, finally we times 7 by 6 which is 42cm²
