SAT Question 64c85440: Linear Inequalities answer and explanation with Desmos solution

Choice D is correct. Placing the parking spaces with the minimum width of $7.5$ feet gives the maximum possible number of parking spaces. Thus, the maximum number that can be placed perpendicular to a $135$-foot-long curb is $\frac{135}{7.5}=18$. Placing the parking spaces with the maximum width of $9$ feet gives the minimum number of parking spaces. Thus, the minimum number that can be placed perpendicular to a $135$-foot-long curb is $\frac{135}{9}=15$. Therefore, if $n$ is the number of parking spaces in the lot, the range of possible values for $n$ is $15\le n\le 18$.