Hey guys, I have a question about a lab I'm doing. I'm getting two positive answers at the end and I'm not sure why. Here's the question:

Cost equations for manufacturing companies are often quadratic in nature. The ACME Widget's cost function for manufacturing widgets is C(x) = x^2 - 10x + 31, where C(x) is the cost of manufacturing x units per week (both in thousands). Find the output for a weekly cost of $15 thousand.

Here's what I have so far:

C(x) = 0 = x^2 - 10x + 16

Did the quadratic formula and got x = 2 and x = 8. Since this is a cost analysis, why am I getting two positive answers? Can someone shed some light on this and help me out a bit? Thanks in advance.