There is S/(v 1+v2)=25.

(25*60)/(S/v2-S/v 1)=20

(v1) 2-3 * v1* v2-(v2) 2 = 0 is substituted for S.

When both sides are divided by (v2)^2.), E 2-3e- 1 = 0.

Solvable e

Suppose my brother ran m laps and my brother ran n laps.

There is m-n = 20.

(n*s)/v2-(m*s)/v 1=25*60

The above four equations can be combined to get the answer.