The total side of the “top” line is 8 + 10 = 18. The total side of the “bottom” line is 45. This makes the ratio 18/45.
Now we are trying to find the “larger” bottom segment, let it be x. Because the lines are parallel, the ratio of the “larger” top and bottom segments is equal to the ratio of the whole top and bottom lines.
Remember Volume of a cube is V=s to the power 3. So in exponential form the answer to your question is V=(14 ft) to the power 3. Or without units. V=(14) to the power 3.