solution 91.
at n=1, new TR-TC = 11-t
at n=2, new TR-TC = 14-2t
at n=3, new TR-TC = 12-3t
at n=4, new TR-TC = 4-4t
substitute values of t from the options most of the time TR-TC< 0 so ignore that t and use the next option. so t = 6, (b) is the answer

this is the answer given by you.but if t=6 then equilibrium no of cows according to mr=mc is 2. which is different from above n . therefore the ans should be a when t=11.because at mc=22 , equilibrium no of cows bought & grazed on the field is equal to no that max village income i.e. 1

Sir
If it isn't asking too much
Can you post the answer key of SSS 2014 and 2015 as well?
The answers posted by the users have different answers to the same questions. So it is kind of confusing