The volume of a rectangular pyramid is 900 cubic centimeters. it has a length of 10 centimeters and a width of 9 centimeters. what is its height

The height of a rectangular pyramid is 30 cm.

volume of rectangular pyramid = (length x width x height) / 3

Given: 
Volume = 900 cm³
Length = 10 cm
Width = 9 cm
Height = ?

V = lwh/3
900 cm³ = (10cm * 9cm * h)/3
900 cm³ * 3 = (90cm² * h)/3 * 3
2700 cm³ = 90cm² * h
2700 cm³/90cm² = 90cm² * h/90 cm²
30 cm = h

to check:
900 cm³ = (10 cm * 9 cm * 30 cm)/3
900 cm³ = 2700 cm³/3
900 cm³ = 900 cm³