Two cars leave from New York and drive in opposite direction

Two cars leave from New York and drive in opposite directions (north and south). The car going north travels at 60 mph. The car going south leaves an hour and a half after the first and goes 80 mph. At what time will the cars be 620 miles apart?

Solution

LET 60*T= THE NORTH CAR.
LET 80(T-1.5)= THE SOUTH CAR.
60T+80(T-1.5)=620
60T+80T-120=620
140T=620+120
140T=740
T=740/140
T=5.2857 HOURS AFTER THE CAR GOING NORTH STARTED THEY WILL BE 620 MILES APART
PROOF:
60*5.2857+80(5.2857-1.5)=620
317.14285+80*3.7857=620
317.14285+302.856=620
620~620