Answer:
Let's assume Navish takes "x" days to complete the work.
Then, Sahir takes "x/3" days to complete the work as he is three times faster than Navish.
As per the problem, Sahir takes 20 days less than Navish to complete the work. So, we can write:
x - 20 = x/3
Multiplying both sides by 3, we get:
3x - 60 = x
Simplifying the above equation, we get:
2x = 60
x = 30
Therefore, Navish takes 30 days to complete the work.