Compound inequality

Question

The width of a rectangle is 4 more than twice the length. If the perimeter of the rectangle has to be between 20 and 50 ft, write a compound inequality for the length of the rectangle. 

Answer 1

w = 2*l+4

perimeter = 2*w + 2*l = 2(2*l+4) + 2*l = 6*l + 8

20 <= 6*l + 8 <= 50

12 <= 6*l <= 42

2 <= l <= 7