Explanation:

The gratuity amount depends upon the tenure of service and last drawn salary. It is calculated according to this formula: Last drawn salary (basic salary plus dearness allowance) X number of completed years of service X 15/26.

• Salary is a consistent payment by an employer to an employee based on a specific position's work and services. If an employer is talking to you about a salary, they usually refer to your base starting salary. A salary package includes additional benefits, incentives and rewards, such as annual and sick leave, car allowance, travel expenses, and further compensation and bonuses. 

Note: DA is calculated as a percentage of the basic salary of a public sector employee.

• It is monthly basic pay * 15/26 * completed years

• DA is added if you are a government employee.

• The minimum year's to be served is 5, there are rulings on the minimum working period to be 4 years and 240 days.

• 15/26, 26 is the days considered in a month for calculation of gratuity

Hence option 3rd is correct.