Answer: 875 cubic feet
Explanation:
Notice that everywhere you look, the figure is 5 feet deep. That is constant everywhere.
Then, you need to cut the figure up into 3 parts to really see what is going on.
Take the left downward-pointing rectangular block and make a vertical cut at its right side. Take the right upward-pointing rectangular block and make a vertical cut at its left side.
That leaves a piece in the middle, 10 feet long, for a total of 3 pieces,
Then you wind up with the picture I have attached.
For the resulting 3 pieces have dimensions
5 * 5 * 10 = 250 cubic feet
5 * 10 * 5 = 250 cubic feet
5 * 5 * 15 = 375 cubic feet
That all adds up to 875 cubic feet.
Hope this helps.