First, fidn the volume of the little cubes that the rectangular prism can hold instide of itself. The formula for volume is length x width x height. This means you have to multiply 1/2 x 1/2 x 1/2. 1/2 x 1/2 x 1/2 = 1/8. Now, since the rectangular prism can hold 840 of these cubes, you need to multiply each cube's volume, 1/8, by 840. 1/8 x 840 = 105.
First you move the parenthesis then you group the like terms after you group the like terms you get which is adding the similar elements and after you add similar elements you get -6m^4-m^3. Srry if this makes no sense