To solve this problem, what we have to do first is to calculate for the volumes of each figure. Let us start from the figure on the left going to the right. Let us call the figures 1 to 4. Formula for volume is:
V = l * w * h
Figure 1:
V1 = 4 * 3 * 1 = 12 unit cubes
Figure 2:
V2 = 3 * 2 * 3 = 18 unit cubes
Figure 3:
V3 = 2 * 2 * 4 = 16 unit cubes
Figure 4:
V4 = 3 * 3 * 3 = 27 unit cubes
The two combinations that would result in 45 total unit cubes would be:
V = V2 + V4 = 18 unit cubes + 27 unit cubes = 45 unit cubes
So the answers are:
Figure 2 and Figure 4