Dear sarvpriye, what is the upper limit of the summation?? and yes, i think you forgot to mention, but i,j,k all should be integers..

 

Anyways, i will tell you the general method, if you are still unable to solve, do tell me the upper limits and i will solve it for you...

 

For the first sigma, take the terms containing i and j our of summation and add the GP for k, with common ratio 1/3, and then take the i term out and add GP for j, with common ratio 1/3, and finally do the same for i.