Let X takes t hr. to travel a distance with speed of 4 kmph. Then distance travelled by X, d=4tkm. Now Y takes (t−2) hr. to complete the same distance with speed of 5 kmph. Then distance d=4t=5(t−2) 4t=5t−10 t=10hr And d=40km Let Z starts t0 time after Y starts then 6(10−2−t0)=40 60−12−6t0=40 6t0=8 t0=