Actually that is a TRAPEZOIDAL prism.
The formula for its volume is
Volume = [((a + b)/2) * height] * length
Where a and b are the parallel sides
a and b are 6 and 8
height =5 and length = 20
Volume = [((6 + 8)/2) * 5] * 20
Volume = 7 * 5 * 20
Volume = 700 cubic centimeters
