Shawn and Rhonda bought identical boxes of stationery. Shawn used hers to write 1-sheet letters and Rhonda used hers to write 3-sheet letters. Shawn used all of the envelopes and had 50 sheets of paper left, while Rhonda used all of the paper and had 50 envelopes left. The number of sheets of paper in each box was:

- 150
- 125
- 120
- 100
- 80