Assuming you mean 7m^3 (meters cubed) of Sand:
Volume = base x width x height
The truck can hold a volume of 2.5 x 1.5 x 1 = 3.75 m^3.
To move 7 m^3 of sand, the truck will have the make two trips. The first trip, the truck will move 3.75 m^3 of sand, and on the second, it will move 7-3.75=3.25 m^3.
