The maximum speed permitted on a certain highway is 65 mi/h, and the minimum is 40 mi/h. The fine for violating these limits is $15 for ever

The maximum speed permitted on a certain highway is 65 mi/h, and the minimum is 40 mi/h. The fine for violating these limits is $15 for every mile above the maximum or below the minimum. Let F(x) be the fine assessed when the speed is x mph. Find a formula for F.