You are given these cash flows for an investment project:
0: -$100
1: +$30
2: +$40
3: +$40
4: +$60
5: +$50
6: +$10
The payback period for this project is _____.
a) between 4 and 5 years
b) between 5 and 6 years
c) between 2 and 3 years
d) between 3 and 4 years