To start off, identify your equation. You know P= 46, and L= 11, so you need to find W=. To do that, first you need to double your length, and width. So, L now equals 22, and W now equals 2W. Now, add W, and L, and it will need to be the original number. Simply subtract 22, from your product, and divide by two, and you'll have W. Here's what the equation should look like.
(2 * 11) + 2W= 46
22 + 2W= 46
46 - 22= 24
2W= 24
W= 12 ft. Or, the width is 12 feet.