Hi Rajat,

unitary method - Technique for solving a problem by first finding the value of a single unit, and then finding the necessary value by multiplying the single unit value.

Here you can see firstly you have to find the single unit then  you can go for your solution, it become little lengthy.

So you can just use this relation K = ^oC + 273 

To find anwer in short time

Hope you got your answer 

Thanks for asking