Question

[ ] +[ ] + [ ]= 30.
fill the boxes using 1,3,5,7,9,11,13,15

Answer 1

Odd numbers don't add up to give you an even number.
It is possible only in case of factorial.

3!+1+3+13+7=30 

3!+3!+3!+3!+3!=30

Answer 2

3!+3!+3!+3!+3!=30
 it is not possible to get the even by summing up the odd numbers