= Solution
At $200\,{}^\circ\mathrm C$, moving from Bi-rich to Sn-rich composition gives \b[$(\mathrm{Bi})$, $(\mathrm{Bi})+L$, $L$, $L+(\beta\mathrm{Sn})$, $(\beta\mathrm{Sn})$]. Approximate <liquid> coexistence compositions read from the diagram are $x_{\rm Sn}\simeq0.33$ on the left and $0.87$ on the right; the coexisting solids lie near their respective pure ends. The stable <Gibbs free energy> follows <solid> curves near the endpoints, two <common-tangent constructions> in the coexistence intervals, and the <liquid> curve between them.
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