A new product has just come onto the market and is a big hit. The success, however, does not last too long. Within a year, sales/day have dropped drastically. a) Given that the number of sales/day, measured in tens of thousands, of the 72 product is represented by the function (t) = -50 (e4-e) after t years, what is the day that the most products are sold? b) How many products were sold on the day?