# Question: please explain the conception and follow the comment how many...

###### Question details

**Please explain the conception and follow the
comment**

How many possible solutions exists for the equation x1 + x2 + x3
= 7 when x1; x2; x3 are

non-negative integers (i.e. x1; x2; x3 2 f0; 1; 2; 3; :::g).