A boat moves downstream at the rate of one km in 71/2 minutes

A boat moves downstream at the rate of one km in 7¹/₂ minutes and upstream at the rate of 5 km an hour. What is the velocity of current ?

Rate downstream = (2/15) x 60 km/hr = 8 km/hr
Rate upstream = 5 km/hr
∴ Velocity of the current = (8 - 5)/2 km/hr = 1.5 km/hr