Respuesta :
Width is 12 inches. Perimeter is add all sides so 15+15 is 30. Next you subtract 30 from 54 which is 24. So with two sides remaining you divide by 2 which is 12, the width is 12 inches.
12 inches because if you know one side is 15, the side opposite of it must be 15 as well. 15+15=30. Then you are left with 24. 24 divided by 2 is 12.