SAT Mathematics Practice Test 4

The total cost y, in dollars, of buying the materials and renting the tools for x days from Store A and Store B is found by substituting the respective values for these stores from the table into the given equation,$y=M+(W+K)x,$ as shown below.Store $A:y=750+(15+65)x=750+80x$

$\text{Store B}:y=600+(25+80)x=600+105x$Thus, the number of days, x, for which the total cost of buying the materials and renting the tools from Store B is less than or equal to the total cost of buying the materials and renting the tools from Store A can be found by solving the inequality $600+105x \leq 750+70x.$ Subtracting $80x$ and 600 from each side of $600+105x \leq 750+70x$ and combining like terms yields $25x \leq 150$.Dividing each side of $25x \leq 150$ by 25 yields $x \leq 6.$Choice B is incorrect. The inequality x ≥ 6 is the number of days for which the total cost of buying the materials and renting the tools from Store B is greater than or equal to the total cost of buying the materials and renting the tools from Store A. Choices C and D are incorrect and may be the result of an error in setting up or simplifying the inequality.