The average annual income (in Rs) of certain agricultural workers is `S` and that of other workers is `T` . The number of agricultural workers is 11 times that of other workers. Then the average monthly income (in Rs) of all the workers is `(S+T)/2` (b) `(S+11 T)/2` (c) `1/(11 S)+T` (d) `(11 S+T)/(12)`