Final answer:
To determine the length of the rectangle, divide the area (36x^2) by the width (3x), resulting in a length of 12x. Hence, the correct answer is 12x.
Step-by-step explanation:
To find the length of the rectangle, we need to divide the area of the rectangle by its width using the formula: Length = Area ÷ Width. In this problem, the area of the rectangle is given as 36x2 and the width is given as 3x. Thus, to find the length, we perform the following calculation:
Length = 36x2 ÷ 3x = 12x
Therefore, the correct answer to the given question is d. 12x