Respuesta :

crisforp
We have the formulas 15 = v1 x t; 21 = v2 x t,  where v1 is the velocity of Terry, v2 is the velocity of Mark and t is the time;
Then v2 = v1 + 2;
v2 x t = (v1 + 2) x t;
So, 21 = 15 + 2xt;
6 = 2xt;
t = 3h;
v1 = 5mph;
v2 = 7mph;