Sylvia is a trusted employee. However, her productivity declines as she works more and more hours each day. As a result, her manager carefully observed her work performance and prepared the following chart. The chart listed the daily number of hours worked by Sylvia followed by a second number, which is the total number of work units to be completed (for example, 1/100 means that one hour of work produces 100 completed work units). 1/120 2/210 3/300 4/370 5/430 6/480 7/520 Based on this information, how many hours should the firm hire Sylvia to work each day, if Sylvia's total cost to the firm is $12 per hour, and each