A building in a city has a rectangular base. The length of the base measures 60 ft less than three times three times the width. The perimeter of this base is 880 ft. What are the dimensions of the base?

The perimeter in this case is:

2L+2W = 840

and the problem says that:

L = 3W-60 Substitute for L in the formula above:

2 (3W-60) + 2W = 840

6W-120+2W = 840 Add 120 on both sides and add W on left:

8W = 960 Divide both sides by 8

W = 120 And the length L is:

L = 3W-60; L = 120 (3) - 60 = 300