The below question contains a paragraph of 6 sentences. The first and the sixth sentences are given in the beginning and end and numbered 1 and 6 respectively. The four sentences in the middle are jumbled and labelled P, Q, R and S. Identify the proper order of these four sentences and mark the correct option.

1. In space navigation it is necessary to make complex calculations.

P. In addition, it has to enter into the moon's orbit at a precise moment.

Q. In other words it has to leave the earth's orbit at a precise moment.

R. A rocket has to follow a precise path.

S. Computers are able to perform extremely complex calculations.

6. A computer can perform the complex calculations which are necessary to work out the rocket's path precisely.