Terry can run 15 miles in the same amount of time it takes Mark to run 21 miles. If Mark runs 2 mph faster than Terry, How fast does Mark run?

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;