Question

a classroom measures 13 m long 9 m wide and 5 m high.calculate the area of the floor

Answer 1

For area, all you need is the length and width.
Multiply them and you get 117

Answer 2

The classroom is theorically a parallelepiped with rectangular base (it would be impossible to be a parallelogram).

So just use the rectangle area formula.

A = b×h = 13×9 = 117 m^2