Chapter 6 - Systems of Equations and Inequalities - 6-1 Solving Systems by Graphing - Practice and Problem-Solving Exercises - Page 364: 31

13 hours

Job1 is $y=9x$, since he earns 9 a week. Job2 is $y=12x-39$. We subtract 39 because of the base cost. Setting them equal, we get $9x=12x-39$. Subtracting 12x from both, we get $-3x=-39$. Dividing by -3, we get $x=13$. So after 13 hours, they will be the same.