Given:

The average salary of all employees in a company = Rs. 5,000 per employee.

The average salary of all 15 employees of technical staff = Rs. 6,500 per employee

The average salary of Non-technical staff = Rs. 4,500 per employee.

Concepts used:

Average salary = (Sum of salaries of all employees)/(Number of employees)

Calculation:

Let the total number of employees in the company be x.

Sum of salaries of all employees = Rs. 5,000 × x = Rs. 5,000x

According to questions

Sum of salaries of technical staff = Rs. 6,500 × 15 = Rs. 97,500

Number of non-technical staff = x – 15  

So, Sum of salaries of non-technical staff = 4,500 × (x – 15) = 4,500x – 67,500

Sum of salaries of all employees = Sum of salaries of technical staff + Sum of salaries of non-technical staff 

⇒ 5,000x = 97,500 + (4,500x – 67,500)

⇒ 5,000x – 4,500x = 97,500 – 67,500

⇒ 500x = 30,000

⇒ x = 60

Number of non-technical employees = 60 – 15 = 45

∴ There are 45 non-technical employees in the company.