Tide removing sand from a beach

The tide removes the sand from a beach at a rate modeled by the function R, given by . A pumping station adds sand to the beach at a rate modeled by the function S, given by .

Both R(t) and S(t) have units of cubic yards per hour and t is measured in hours for . At time , the beach contains 2500 cubic yards of sand.

How much sand will the tide remove from the beach during this 6 hour period. Indicate units of measure. Write an expression for the total number of cubic yards of sand on the beach at time t.

Any help is appreciated, thanks.