It's a system of equations. 2 equations, 2 unknowns. The number of boxes of 10. And the number of boxes of 100 are your unknowns. Call these x and y respectively. (Or your x1 x2)
The two equations come from the following conditions:
- He has 3 more boxes with 100 paper clips than he has boxes with 10 paper clips.
- He has 2 fewer paper clips left over than he has numbers of boxes with 100 paper clips
As an aside. This problem is dumb. Fuck brian. Fuck his paperclips.