If you draw a perpendicular to CD from point A or point B, you will create a right triangle with one leg 5 and hypotenuse (BC or DA) 13. The other leg of this triangle is the height of the trapezoid:
... h = √(13² -5²) = 12
The area is this height multiplied by the average base length:
... Area = (12 cm)×(10 cm +20 cm )/2 = 180 cm²
