84 is a pure number and, as a number, it has no dimensions.
72 x 84
80%
1,2,3,4,6,7,12,14,21,28,42,84
72" x 84"
You can't tell the dimensions from the perimeter. There are an infinite number of rectangles, with different dimensions, that all have the same perimeter. If it's 168, then the only thing you can be sure of is that the length and width add up to 84, but you can't tell what either of those dimensions must be.
None. You need a third dimension to get a volume.
That depends on how many faces this particular prism has.
One dimension is 84 inches. For the others, you would need to measure the sign.
72" Wide x 84" Long
84
You have to multiply the two dimensions to get the area. In this case the answer will be 84 square feet. That would be 9.33 square yards.