The question is there are three blanks like this ___ + ___ + ___ =30 and we have to fill the blanks?

First of all by understanding the basic concept of the math:

ODD NO. ODD NO = EVEN NO.
AND
ODD ODD ODD = ODD NO.
While
30 is even no. And the numers given are all odd.
Since cude addition of odd number is itself of odd no. So even number as a product is not possible.

Ok now geting to the question u can try this:
15 + 13 + (3-1)=30
13 + 11 + (7-1)=30
& So on.....
Else it is not possible....