The wall of a house is $18\ \text{cm}$ of brick, of thermal conductivity $0.60\ \text{W/(m K)}$, covered on the outside by $6.0\ \text{cm}$ of foam insulation, of thermal conductivity $0.050\ \text{W/(m K)}$. On a cold night the inner face of the brick is at $25\ ^\circ\text{C}$ and the outer face of the foam is at $-5\ ^\circ\text{C}$. In the steady state, what is the temperature where the brick meets the foam? Give the answer in $^\circ\text{C}$.