Integration helps when trying to multiply units into a problem. For example, if a problem with rate, formula_2, needs an answer with just distance, one solution is to integrate with respect to time. This means multiplying in time to cancel the time in formula_3. This is done by adding small slices of the rate graph together. The slices are close to zero in width, but adding them together indefinitely makes them add up to a whole. This is called a Riemann sum.