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## Homework Statement

How thick a concrete wall would be needed to give the same insulating value as 3.5 inches of fiberglass?

## Homework Equations

Q = -A·k·ΔT/Δx

k = -Q·Δx/A·ΔT

## The Attempt at a Solution

So here, k is equal to the insulating value, and since I want the insulating value to be the same for the concrete wall and fiberglass, I would have the equation

-Q·3.5/A·ΔT = -Q·Δx/A·ΔT

Since it seems that area and change in temp are the same in both cases, I got

Q·3.5 = Q·Δx

Which is where I got stuck. Would the Q (heat flow) cancel?