Since the formula for the perimeter is 2l+2w=290 (given that the length=l and the width is w), we plug 84 in for l to get (2)(84)+2w=290. Next, we multiply it out to get 168+2w=290 and we subtract 168 from both sides to get 122=2w. Dividing 2 from both sides, we get 61=w.