the length of the box is represented by (8m2)
does that mean 8m^2?
in English that would be 8 times m^2 or 8 * m * m.
if that is true, then the volume of the box would be equal to (8*m^2)^3 which is equal to 8^3 * m^6 which is then simplified further to 512 * m^6 which can also be written as 512m^6.
if we assume that m is 3, then the side of the box is equal to 8 * 9 which is equal to 72 and that is cubed to get 373248.
working that out algebraically, it would look like this:
(8*3^2)^3 equals 8^3 * (3^2)^3 which is equal to 8^3 * 3^6 which is equal to 512 * 729 which is equal to 373248