Calculate the surface area of a trapezium of parallel sides 5cm8cm and other side 10cm?

trapezium surface area = 1/2 * (parallel-side-1 + parallel-side-2) * height

= 13/2 * height

height (assuming isosceles trapezium) = sqrt (10 squared - (3/2) squared)

= sqrt (100 - 9/4) ~ 10

area ~ 65 cm squared.