Volume of a rectangular prism is length * width * height.
The figure can be broken into 3 different prisms. Left to right, I'd label them 1st tower, connecting base, 2nd tower.
I'll do the 2nd tower first since it has the most measurements. 5 * 5 * 12 = 25 * 12 = 300
The first and second towers are congruent so they have the same measurements; we just do 300 + 300 to find their volumes. It's 600.
Now, to find the connecting piece. The whole bottom length of this "U" shaped figure is 18 but the two towers have lengths of 5. To find the base of the portion we're looking for, we do 18 - 2(5) = 18 - 10 = 8. To find the height, we take away the top part of the second tower (7 m) from the whole height (12 m). 12 - 7 = 5. The width is given by the towers so we have what we need to solve.
8 * 5 * 5 = 40 * 5 = 200
Now add the volumes all together.
600 + 200 = 800
The figure has a volume of 800 cubic meters or 800 m³.