8. The payback period of an investment is defined as:

a. the number of years required for the cumulative cash flows from a project to equal the average investment in the project, when depreciation is considered.

b. the number of years required for the cumulative cash flows from a project to equal the initial outlay.

c. the number of years required for cumulative profits from a project to equal the initial outlay.

d. a period of time sufficient to earn a rate of return equal to the firm's cost of capital.