The employee will have to wait for 4 years to get the salary.
Step-by-step explanation:
Given,
The salary pr month = 400BD
10% salary will be raised for the 3 years.
To find the salary 600BD per month
For, 1st year, the salary is = 400BD
For, 2nd year, the salary will be = 400 + 400 × 10%
=440BD
For, 3rd year, the salary will be = 440 + 440 × 10%
= 484BD
For, 4th year, the salary will be = 484 + 484 ×10%
= 532.4BD
Next additional year the salary will be raised 20% per year
so, for 5th year, the salary will be = 532.4 + 532.4 ×20%
=638.88BD
Hence, in 5th year the salary will be more than 600BD per month
That means, the employee has to wait for 4 years after joining to get the salary.