Among five iron balls P, Q, R, S and T, the weight of Q is 5 kg, which is double the weight of P. The weight of S is half the weight of T. The weight of R is equal to the weight of P and Q taken together. The weight of T is four times the weight of R. What is the weight of S?

A

10 kg

B

30 kg

C

15 kg

D

7.5 kg