Let x be the width of the room. If the width is 3.5 feet less than the length, then the length is x+3.5. The perimeter is x+x+x+3.5+x+3.5=4x+7.
Since the perimeter is equal to 67, then 4x+7=67, 4x=60, x=60÷4, x=15 ft and x+3.5=15+3.5=18.5 ft.
Answer: the width is 15 ft, the length is 18.5 ft.