Two men at points R and S, 76 km, apart, set out at the same time to walk towards each other. The man at R walks uniformly at the rate of `4 1/2` km/hr`;` the man at S walks at the constant rate of `3 1/4k m//h r` for the first at `3 3/4` km/hr for the second hour, and so on in arithmetic progression. If the men meet `x` km nearer R than S in an integral number of hours, then `x` is `4` b. `6` c. `8` d. `10`