SAT Question 0e40dfb0: Area and Volume answer and explanation with Desmos solution

Choice D is correct. The area of a rectangle is given by $lw$, where $l$ is the length of the rectangle and $w$ is the width of the rectangle. It's given that a rectangle has a length of $3$ units and a width of $39$ units. It follows that the area of the rectangle is $3\cdot 39$ square units. Therefore, the expression that gives the area, in square units, of this rectangle, is $3\cdot 39$.