Need Help Big debate with Finance professor.

I am in a Principles of Finance class. The teacher is very smart, and knowledgeable, but not a very good teacher. My class has been having this month long debate/argument with her over a specific problem. She uses Mcgraw hill to assign us work, but often we find ourselves very confused and the software getting it wrong, but not giving a logical explanation of the answer they give. Anyways here is the question.

Mr. Dell has $120 in income this year and will have zero income next year. The expected return from investing in the stock market is 10 percent a year. Mr. Dell also has an investment opportunity-having the same risk as the market in which he can invest $40 this year and receive $90 next year. Suppose Mr. Dell consumes $50 this year and invest in the project. What is the NPV of the investment opportunity?

What is the answer?

The answer the students keep getting is 41.82, but the answer she, and the software is giving is 31.82. We are using the 40 because it is asking about the NPV of the investment opportunity as -C0 (initial investment) plus C1 (90) divided by R + 1.

The software and her are saying that -C0 is the 50 he consumed.