Angie Xu has converted her garage into a greenhouse with long tables where she plans to grow flower plants from seeds to sell in the spring at the downtown market. She will plant two types of flowers from seeds-daisies and impatiens. A tray of impatiens takes up 216 square inches of table space and a tray of daisies takes up 324 square inches of table space, and there is 43,200 square inches of available space. Impatiens are more temperamental to grow than daisies so Angie will have to spend more time cultivating them-on average 8 minutes per tray of impatiens and 4 minutes per tray of daisies each week-and she has a total of 18 hours available each week to grow her flowers. If Angie sells impatiens for $6 per tray and daisies for $4 per tray, she wants to know how many trays of each flower she should grow in order to maximize her revenue.

a. Formulate a linear programming model for this problem and solve using the computer.

b. If Angie can increase the time she spends each week with her flowers by 4 hours, how much more revenue might she get?