Answer: Crystal will earn $11.81.
Explanation:
Since we have given that
Cost per hour mowing lawns = $5.25
Let the number of hours be 'h'.
Let the amount of money be 'm'
So, According to question, we get

Here h = 2 hours and 15 minutes
So,

So, Crystal will earn if she works for 2 hours and 15 minutes will be

Hence, Crystal will earn $11.81.