Answer:
860.9 m³
Explanation:
We can obtain the volume of the composite figure by subtracting the volume of cylinder from the volume of cuboid.
Cuboid or rectangular prism:
 l = 10 m
 w = 10 m
 h = 12 m
 

 = 10 * 10 * 12
 = 1200 m³
Cylinder:
 r = 3 m
 h = height of the cuboid = 12 m
 

 = 3.14 * 3 * 3 * 12
 = 339.1 m³
Volume of composite figure = 1200 - 339.1
 = 860.9 m³