It is necessary to find the volume of a rectangular prism in which the length is 12 dm, width 8 dm, height 10 dm.

First of all, note that the rectangular prism in this case is nothing more than a rectangular parallelepiped.

Secondly, we need to write down a formula by which we can determine the volume of a rectangular prism:

V = a * b * c,

where a is the length of the base of the prism;
b is the width of the base of the prism;
c is the height of the prism.

We use the indicated formula and calculate the volume of a rectangular prism with the parameters specified in the problem statement:

V = a * b * c = 12 * 8 * 10 = 960 (dm 3).

Answer: 960 dm 3.