Choice C is correct. It's given that there is a linear relationship between a plumber's hours of labor, $h$ , and the plumber's total charge $f(h)$ , in dollars. It follows that the relationship can be represented by an equation of the form $f(h) = mh + b$, where $m$ is the rate of change of the function $f$ and $b$ is a constant. The rate of change of $f$ can be calculated by dividing the difference in two values of $f(h)$ by the difference in the corresponding values of $h$ . Based on the values given in the table, the rate of change of $f$ is $\dfrac{285-155}{3 - 1}$, or $65$ . Substituting $65$ for $m$ in the equation $f(h) = mh + b$ yields $f(h) = 65h + b$. The value of b can be found by substituting any value of h and its corresponding value of $f(h)$ for $h$ and $f(h)$ , respectively, in this equation. Substituting $1$ for $h$ and $155$ for $f(h)$ yields $155 = 651 + b$, or $155 = 65 + b$. Subtracting $65$ from both sides of this equation yields $90 = b$. Substituting $90$ for $b$ in the equation $f(h) = 65h + b$ yields $f(h) = 65h + 90$.

Choice A is incorrect and may result from conceptual or calculation errors.

Choice B is incorrect and may result from conceptual or calculation errors.

Choice D is incorrect and may result from conceptual or calculation errors.