Answer:
The length of the rectangle is 7x + 27
Explanation:
Given;
area of the rectangle, A = 21x + 81 units²
width of the rectangle, w = 3 units
let the length of the rectangle, = L
Area of the rectangle = length x width
A = L x w
21x + 81 = 3L
L = ¹/₃(21x + 81)
L = 7x + 27
Therefore, the length of the rectangle is 7x + 27