A thin rectangular plate, $0 \leq x \leq a, 0 \leq y \leq b$, with negligible heat loss from its sides, has the following boundary conditions:
$$
\begin{array}{ll}
x=0, & 0<y<b: T=300 \mathrm{~K} \\
x=a, & 0<y<b: T=400 \mathrm{~K} \\
y=0, & 0<x<a: q_{y}=0 \text { (insulated) } \\
y=b, & 0<x<a: T=500 \mathrm{~K}
\end{array}
$$
(i) Determine the steady-state temperature distribution.
(ii) If $a=b$, determine the center temperature.