In the equation \( y = 150x + 50 \), the variable \( y \) represents the total cost, \( x \) represents the number of hours Dr. Shah spends at the home, and the coefficients indicate the relationship between these variables.
The y-intercept of this equation occurs when \( x = 0 \). If we substitute \( x = 0 \) into the equation, we get:
\[ y = 150(0) + 50 = 50 \]
This means that when no hours are spent (0 hours), the total cost \( y \) is $50.
In the context of the situation, this y-intercept represents the fixed cost associated with the visit, which is likely a base fee that is charged regardless of the time spent at the patient's home.
Therefore, the y-intercept represents:
the extra amount after the hourly rate.
So the correct answer is: the extra amount after the hourly rate.