If you would like to know the average speed of the delivery truck, you can calculate this using the following steps:
205 miles ... 3 1/2 hours = 7/2 hours
x miles = ? ... 1 hour
205 * 1 = 7/2 * x
205 = 7/2 * x
x = 205 * 2/7
x = 58.6 miles
The correct result would be 58.6 miles per hour.