The average salary of all the 60 employees in an office is Rs. 12,000 per month. if the number of executives is twice the number of non executives employees, then the average salary of all the non executives employees is

No. of executives / No. of non- executives
= 2 / 1
Therefore
Number of executives = 40
and number of non executives employees = 20
now , go through the options
Total salary = 40 x salary of executives + 20 x salary of non-executives
60 x 12000 = 40 x k + 20 x l, here k, l are unknowns
so we con't determine the required average salary