Solution (source code)

= Solution
{c}

Inward <heat flux> at the left end points in the positive $x$ direction, so the <boundary conditions> are
$$
-kT_x(0,t)=Q,\qquad T(2\ell,t)=0.
$$
For uniform <thermal conductivity>, the steady <heat equation> gives $T_s''=0$. The <heat flux> is constant and equal to $Q$, so $T_s'=-Q/k$. Imposing the right-end temperature gives
$$
\boxed{T_s(x)=\frac Qk(2\ell-x).}
$$