Note: A maximum number of 4 points are available for this question. Part A is worth 1 point. Part B is worth 1 point. Part C is worth 2 points. Mr. Martinez hires a plumber to fix his kitchen sink. The plumber charges a one-time fee of $45 and an additional $15 for parts. He also charges $40 for each hour he works.

The cost of hiring the plumber can be represented by a linear function. Identify the rate of change and initial value of this function. Explain what these values represent in terms of the situation.