Answer:
The $50 fixed fee the plumber charges
Explanation:
The constant rate in this situation refers to the part of the plumber's charges that remains the same regardless of the number of hours worked. In this case, the constant rate is the fixed fee of $50, since this fee remains the same regardless of how many hours the plumber works.
The $60 per hour rate is not constant, as it varies based on the number of hours worked. The 6 hours the plumber works is not the constant rate, as it refers to the amount of time worked and not a fixed fee. The total cost of $410 is not the constant rate, as it includes both the fixed fee and the hourly rate charged by the plumber.
Therefore, the constant rate in this situation is the $50 fixed fee that the plumber charges.