1. **Problem Statement:** We need to match the correct graph to the story of a plumber charging a fixed fee plus a fixed amount per hour. 2. **Understanding the problem:** The total cost $y$ depends on the time $x$ the job takes. The plumber charges a fixed fee (a constant) plus a fixed rate per hour (a constant multiplied by $x$). 3. **Formula:** The total cost can be expressed as: $$y = f + r \times x$$ where $f$ is the fixed fee and $r$ is the rate per hour. 4. **Graph characteristics:** - Since $y$ is a linear function of $x$ (fixed fee plus a constant times $x$), the graph should be a straight line with a positive slope. - The fixed fee $f$ is the y-intercept (cost when $x=0$). 5. **Matching graphs:** - Graph A is exponential, which does not fit a fixed fee plus fixed hourly rate. - Graph B is a step graph, which would represent costs increasing in jumps, not a fixed rate. - Graph C is a straight line with positive slope, matching the linear cost model. - Graph D is wave-like, which does not fit the cost model. **Final answer:** The correct graph is **Graph C**.