suppose ABCD is the trapezuim with AB parallel to CD. AB= 13, CD =25, BC=15, AD=15. Draw a line parallel to AD passing through point B. you will get a parallelogram and a triangle. sum up their areas.
How do I find the area of a trapezium whose paralle sides are 25 cm, 13 cm & the other two sides are 15 cm each?
Draw perpendicular line segments from one of the summit vertices to to the base. That is an altitude(hight). It is in a right triangle with hypotenuse 13 and base 5.
Carry on from there.
more over the triangle you get is isoceles so you can use pythagoras theorem to find the height of the triangle( which is equal to the distance between the parallel sides)