A starts 3 Minutes after B for a place 4.5 km distant. B, on reaching his destination, immediately returns and after walking a km meets A. If A can walk 1 Km in 18 minutes,then what is B's speed?

P__________3.5Km__________M__1km____Q
Speed of A = 1 km in 18 min = $$\frac{{1000}}{{18}}$$  = 55.55 m/min.
When A travels 3.5 km. B already has been traveled (4.5 + 1) = 5.5 km.
A will take time to travel 3.5 km = $$\frac{{3500}}{{55.55}}$$  = 63 min.
So, B will take 66 min to travel 5.5 km (As B has started 3 min before of A)
Thus, speed of B = $$\frac{{5500}}{{66}}$$  = 83.33 m/min = 5 km/h