[ ]+[ ]+[ ]=30
Fill the boxes using this
(1,3,5,7,9,11,13,15)
Note: you can also repeat the number twice
I don't see any way to solve this one. And you have 3 boxes and all options are odd numbers and you have an even number on the RHS
PROBABLY THERE IS SOME TECHNIQUE
Or you need to some smartness here
3 factorial gives 6 so 1 solution that I see here is
(3!)+(15)+(9)=30