Call the number of hours of labor x.
A flat rate of $500 -> just $500.
$50 for each hour of labor -> 50x (for x hours)
Therefore, we can represent the amount needed for x hours of labor as the function : 500 + 50x.
We substitute :
20 hours of labor = 500 + 50 x 20 = $1500
50 hours of labor = 500 + 50 x 50 = $3000