Explanation:

Let the number of workers = x
Given that average salary of all the workers = Rs.8000
Then, total salary of all workers = 8000x
Given that average salary of 7 technicians is Rs.12000
= Total salary of 7 technicians = 7 × 12000 = 84000
Count of the rest of the employees = (x - 7)
Average salary of the rest of the employees = Rs.6000
Total salary of the rest of the employees = (x - 7)(6000)
8000x = 84000 + (x - 7)(6000)
= 8x = 84 + (x - 7)(6)
= 8x = 84 + 6x - 42
= 2x = 42
= x = 422 = 21

Hence, option 2 is the correct answer.