An oblique prism has trapezoidal bases. which expression represents the volume of the prism? 10x3 cubic units 15x2 cubic units 20x3 cubic units 30x2 cubic units

This is the concept of volume of solid figures, the volume of a given figure is given by:
volume=(base area)*(height)
In our case the base area will be given by the area of the trapezoid. Which is:
Area=1/2*h*(a+b)
height,h=x 
a=x
b=2x
thus;
Area=1/2*x*(2x+x)=3/2x^2
Given that the height of the prism is 20 units, the volume will be:
V=(3/2 x^2*20)
V=30x^2 cubic units
The answer is 30x^2 cubic units

How many is in each case if there is 12 in each case it would be 40