A contractor charged a client $240 to paint a fence, estimating that the work would take a certain number of hours to complete. However, the contractor completed the work 2 hours earlier than estimated, resulting in a $6 increase in his per hour rate. How many hours did the contractor originally estimate the work would take?

When I factorize the quadratic equation, where t is time, I get (t-12)(t+10), i.e., t=12 and t=-10. yet, the answer here is 10. Some help please? Thanks!