Mr. Powers determines his sons allowance based on the following situations: The amount of money they receive in a week is directly proportional to the number of hours of work they have done in the yard and inversely proportional to $5 − \text{GPA}$ where GPA is the grade point average from the last report card. Clark received $\$14.40$ since his last report card had a GPA of $3.5$, and he worked $10$ hours in the yard during the week.

1. Find the formula that Mr. Powers uses to determine the amount of money he will give his sons each week.

   Hint (a):

   Now find k with the given information.

2. William worked $15$ hours in the yard and received $$20$. What was William’s GPA from his last report card?

   Hint (b):

   Use the equation you found in part (a).