Let speed of A=x and that of B = y (mph) B does journey in 7/8 of the time that A does. Hence y=(8/7)x

A takes 4hr so AB=4x Let t= time A has travelled when they meet. So B has travelled t-2 hr

When they meet distance gone by A + distance gone by B = AB=4x

Hence xt+y(t-2)=4x But y=(8/7)x Sub for y and solve for t