SAT Mathematics Practice Test 4

The total cost, y, of buying the materials and renting the tools in terms of the number of days, $\mathit{x}$,is given as $\mathit{y}=\mathit{M}+\left(\mathit{W}+\mathit{K}\right)\mathit{x}.$ If this relationship is graphed in the xy-plane, the slope of the graph is equal to $\mathit{W}+\mathit{K}$,which is the daily rental cost of the wheelbarrow plus the daily rental cost of the concrete mixer, that is, the total daily rental costs of the tools.
Choice A is incorrect because the total cost of the project is y. Choice B is incorrect because the total cost of the materials is M, which is the y-intercept of the graph of $\mathit{y}=\mathit{M}+\left(\mathit{W}+\mathit{K}\right)\mathit{x}.$ Choice C is incorrect because the total daily cost of the project is the total cost of the project divided by the total number of days the project took and, since materials cost more than 0 dollars, this is not the same as the total daily rental costs.