The walking speed ratio of A and B is 9:7AB. Two people leave from a and b at the same time. If they go in opposite directions and meet for 0.5 hours, if they go in the same direction at the same time, then a.
Let the speed of AB be 9m and 7m respectively, then the distance between A and B is 0.5*(9m+7m)=8m.
Let A spend x hours chasing B in the same direction at the same time, the column equation is 7mx+8m=9mx, m eliminates 7x+8=9x, and the solution is x=4.
That is to say, going in the same direction at the same time, it takes 4 hours for A to chase B.