John has 3 boxes.  Each box is 5 inches by 6 inches by 4 inches.  The walls are 1 inch thick.  What is the total inner volume of all 3 boxes?
The walls subtract 2*1=
<gadget id="calculator">2*1</gadget>
<output>2</output>
2 inches from each dimension.
So each box has 5-2=
<gadget id="calculator">5-2</gadget>
<output>3</output>
3 inch width.
It also has a 6-2=
<gadget id="calculator">6-2</gadget>
<output>4</output>
4 inch height.
Finally, it has a 4-2=
<gadget id="calculator">4-2</gadget>
<output>2</output>
2 inch depth.
So the inner volume of one box is 4*3*2=
<gadget id="calculator">4*3*2</gadget>
<output>24</output>
24 cubic inches.
So in total the inner volume of the 3 boxes is 3*24=
<gadget id="calculator">3*24</gadget>
<output>72</output>
72 cubic inches.

<result>72</result>