A man drives 60 mph for 3 hours.  How fast would he have to drive over the next 2 hours to get an average speed of 70 mph?
To have an average speed of 70 mph over 5 hours he needs to travel 70*5=<T>multiply(70, 5)=350 miles.
He drove 60*3=<T>multiply(60, 3)=180 miles in the first 3 hours
He needs to travel another 350-180=<T>subtract(350, 180)=170 miles over the next 2 hours.
His speed needs to be 170/2=<T>divide(170, 2)=85.0 mph
