 Here we have, again, a wall made up of three different layers. The first layer is wood siding, which is outside, obviously. And its r value is given as 0.81, whatever the thickness might be of that wood siding. And we have a second layer of fiberglass. And this fiberglass thickness is given as 5 inches. And its r value is given as 3.7 per inch. So we are using 5 inches. 5 times 3.7 would be 18.50. And we have a third layer of a drywall. And this drywall has an r value of 0.45, half inch drywall. When you add all these three layers up, you get a total r value of 19.76. So the answer is 19.76 degrees Fahrenheit foot square hour over BTU. This is the composite r value.