Question 837566
This is to help you start, but is not the whole solution:


r = one car's rate
r+16 = the other car's rate


_____________speed___________time________distance
FastCar______r+16_____________4_________(___)
SlowCar_______r_______________4_________(___)
Total_____________________________________720


The uniform rates travel equation is R*T=D, where R is rate, T is time, and D is distance.  The unit for R must be consistent with the units of T and D.


Do you see what to do next and to finish?