Explanation:

Let the distance be x km and speed be y kmph;
x/y = 25 => x =25y; --------eq.(i.)
(x-200)/(4y/5) = 25  =>x-200 = 20y; ---- eq.(ii.)
Put value of x from eq.(i) to eq.(ii.)-
25y-200 = 20y;
5y = 200 => y=40  kmph