OG详解-OG3 数学1 Q9

Choice A is correct. It’s given that the electrician charges a onetime fee plus an hourly rate. It’s also given that the graph represents the total charge, in dollars, for x  hours of work. This graph shows a linear relationship in the xy-plane. Thus, the  total charge y , in dollars, for x hours of work can be represented as y = mx + b,  where m is the slope and (0, b) is they-intercept of the graph of the equation in the xy-plane. Since the given graph represents the total charge, in dollars, by an electrician for x hours of work, it follows that its slope is m, or the electrician’s hourly rate.
Choice B is incorrect. The electrician’s onetime fee is represented by the y-coordinate of they-intercept, not the slope, of the graph. Choice C is incorrect  and may result from conceptual errors. Choice D is incorrect and may result from conceptual errors.