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
