At noon a private plane left Austin for Los Angelas, 2100 km away, flying at 500 km/h. One hour later a jet left Los Angelas for Austin at 700 km/h. At what time do they pass each other?

The distance covered by the private plane is given by:



The distance covered by the jet is given by:



Since it departed 1 hour later (at t = 1, it hasn't covered any distance).

The sum of both distances now give a total of 2100 km, if they meet (the part covered by the jet and the part covered by the private plane equal the total distance).



Just substitute the equations in there and find t, the time they took to meet each other. Then add that t in hours to noon to get the time they meet.