Since ABCF is a rectangle, angle AFC is a right angle. Angle CFE is also a right angle. Since angle DCF is also a right angle, then trapezium CDEF has parallel sides CD and EF.
BC + CD = BD
4 cm + CD = 9 cm
CD = 5 cm
EF = 3 cm
Sides CD and EF are the parallel bases of the trapezium. Side CF is the height of the trapezium.
area of trapezium = (base1 + base2)h/2
area = (5 cm + 3 cm)(6 cm)/2
area = (8 cm)(6 cm)/2
area = 24 cm^2
