To find the equation in slope-intercept form \( y = mx + b \), where \( y \) represents the total earnings, \( x \) represents the number of cars sold, \( m \) is the slope (the commission earned per car sold), and \( b \) is the weekly salary.
Let's denote:
- \( y_1 = 1875 \) when \( x_1 = 5 \) (for the first employee)
- \( y_2 = 2150 \) when \( x_2 = 6 \) (for the second employee)
We can set up a system of equations based on the given information:
- \( 1,875 = m \cdot 5 + b \)
- \( 2,150 = m \cdot 6 + b \)
To solve these equations, we can start by eliminating \( b \):
From the first equation: \[ b = 1875 - 5m \]
Now, substitute \( b \) into the second equation: \[ 2150 = 6m + (1875 - 5m) \]
This simplifies to: \[ 2150 = 6m + 1875 - 5m \] \[ 2150 = m + 1875 \] \[ m = 2150 - 1875 = 275 \]
Now that we have the value of \( m \), we can substitute it back to find \( b \): \[ b = 1875 - 5 \cdot 275 \] \[ b = 1875 - 1375 = 500 \]
Now, we have \( m = 275 \) and \( b = 500 \). The equation in slope-intercept form is: \[ y = 275x + 500 \]
Therefore, the equation representing the earnings of an employee based on the number of cars sold is: \[ \boxed{y = 275x + 500} \]