4. Tourists visiting an island resort contracted a mystery illness over a 15-day period. The health authorities recorded the rate of new cases per day and some of the rates are listed in the table below. N(t) Day New cases per day a. Explain the meaning of J N(t) dt in the context of the problem. b. Use a left Riemann sum, with the four subintervals indicated by the data in the table, to approximate N(t) dt. Use appropriate units