#### Answer

The net earnings of the two jobs will be the same at 13 hours of work. At 13 hours of work, both jobs will have made 117 dollars.

#### Work Step by Step

Job one can be represented by the equation: y= 9x
Job two can be represented by the equation: y=12x-39
Set the two equations to equal one another:
$9x = 12x-39 \\
9x =12x-39\\
0=3x-39 \\
39=3x\\
x=13$
Once you have your x value, plug it in to one of the original equations of your choosing:
$9(13)= 117$ dollars