Answer: Crystal would earn $20.625 by working 3 hours and 45 minutes.
Explanation:
Since we have given that
Cost per hour for mowing lawns = $5.50
Let h be the number of hours.
Let the amount of money be 'm'.
So, the equation would be

If number of hours = 3 hours 45 minutes =

So, Amount of money earned by Crystal would be

Hence, Crystal would earn $20.625 by working 3 hours and 45 minutes.