A man can walk uphill at the rate of `2 1/2` km/hr and downhill at the rate of `3 1/4` km/hr. If the total time required to walk a certain distance up the hill and return to the starting point was 4 hr 36 min, then what was the distance walked up the hill by the man? `4\ k m` b. `4 1/2k m` c. `5 1/2k m` d. `6 1/2k m`