To start, we need to know the equation that correlates the volume of a pyramid with its height
this formula is given by the product of the sides of its base with the height divided by 3.
V = h x (B x b)/3
In your example, we have the volume equals to 72 in^3(the V in the equation), the bigger side of the base is equal to 6 in(the B in the equation), and the smaller side of the base is equal to 4 in(the b in the equation)
Just pluggin it in the equation gives us the following formula:
72 = h x (4 x 6)/3
Solving the equation e get
72 = h x 24/3
72 = h x 8
h = 72/8
h = 9
Then, you have your answer!
The height in your equation is 9 inches!
x = 9in.