first check the endpoints. that is, find f(-1) and f(5).

then search for the critical values. that is, find f'(t) and set it equal to zero and solve for t. then find all f(c) where c represents a critical value, that is, one of the t's you solved for just before. which ever one of these values is the greatest (you include the endpoints as well) is the absolute max, whichever is the lowest is the absolute min

can you continue?