to find the volume, break the figure into 2 parts, the longer rectangle across the bottom and then the smaller square on top.
volume = L x W x H
the lower rectangle has L=20, W =5 and H = 5
Volume = 20 * 5 * 5 = 500 cubic inches
the top square has L = 5, W = 5 and H = 5
volume = 5*5*5 = 125 cubic inches
total volume = 500+125 = 625 cubic inches