Length of the two parallel sides of a trapezium are 8.5 cm and 11.5 cm and its height is 4.2 cm.
Area of a trapezium = (1/2) x sum of lengths of parallel sides x height
= (1/2) x (8.5 + 11.5) x 4.2
= (1/2) x 20 x 4.2
= 10 x 4.2
= 42 sq. cm
∴ The area of the trapezium is 42 sq. cm.