Suppose that the frequencies of human and dog are h 1=2x and h2=3x, respectively, and the stride is A 1=2y and A2=y, respectively.

Then the velocities are v1= h1* a1= 4xy and V2=h2*A2=3xy, respectively.

Then the catch-up time is t =10y/(4xy-3xy) =10/x.

Then, the dog ran away again L=V2*t=3xy* 10/x=30y.

So, I ran another 30 steps.