It is given in the question that the area of the glass window of a room is $10 m^{2}$ and thickness is 2 mm, the outer and temperature is 40^\circ C , and the inner temperature is $20^\circ \mathrm{C}$ . it is also given that the thermal conductivity of glass in S.I unit is 0.2. Then we have to find the heat flowing in the room per second.

We know that the heat flowing through the room per second is given by $\frac{Q}{t} = \frac{A \cdot K \Delta t}{dx} .$
Here, $\frac{Q}{t}$ is representing the heat flowing in the room per second, A is the area of the glass window, K is the thermal conductivity of glass in S.I unit, $\Delta t$ is the temperature change, dx is the thickness of the glass window.
Here we will convert the thickness of the glass window into the meter. We know that $1 \mathrm{m} = 10^{3} \mathrm{mm}$ we get-

$2 \text{ mm} = 2 \times 10^{-3} \text{ m}$

The temperature change $\Delta t$ is given by outer temperature - inner temperature. We get-

$\Delta t = 40^\circ - 20^\circ = 20^\circ \mathrm{C}$

On putting the values of $A, K, dx, \Delta t$ in $\frac{Q}{t}$ , we get-

$\frac{Q}{t} = \frac{10 \times 0.2 \times 20}{2 \times 10^{-3}}$

Here the value of t in L.H.S is one second, we get-

$Q = \frac{10 \times 0.2 \times 20}{2 \times 10^{-3}}$ $Q = \frac{10^{\times} \times 2 \times 2}{0.0002}$ $Q = \frac{40}{0.0002} = 20000 \, J$ $Q = 2 \times 10^{4} \, J$

So, the flow of heat in the room per second will be $Q = 2 \times 10^{4} J$ .