The function will be

where y is the balance, and x is the number of month.
The raph will be a line on the xy-plain which starts at the point (0, 360), and end in the point (72, 0).
Hope it helps.
Answer is 7950,72. You can solve it's task on calculator.
69 square feet is the answer
15,9,8 can be divided by 3
so, the greatest number of fruit in each basket is 3