Two conducting slabs of heat conductivity $K_1$ and $K_2$ are joined as shown in fig. The temp. at ends of the slabs are $\theta_1$ and $\theta_2({\theta_1}>{\theta_2})$ the, final temp. ( $\theta_m$ ) of junction is : <br>

Question

( A ) NONE
( B ) $\frac{K_1 \theta_1+K_2\theta_2}{K_1+K_2}$
( C ) $\frac{K_1 \theta_2-K_2\theta_1}{K_1+K_2}$
( D ) $\frac{K_1 \theta_2+K_2\theta_1}{K_1+K_2}$