If 9+10=21 what is 21-9 ?

Which of the following points is collinear with (-2,1) and (0,3)

10 ! a train starts from grand city and travels toward belleville 388 miles away. at the same time, a train starts from belleville and runs at the rate of 47 miles per hour toward grand city. they pass each other 4 hours later. find the rate of the train from grand city.

How do i simply this expression (quadratic formula basis) on a ti-84 or normal calculator?