Solution
= Solution
Apply the <lever rule> on the $779^\circ\mathrm C$ solid tie line. All compositions are <copper> <mass> percentages:
$$
\boxed{w_\alpha=\frac{92-28}{92-9}=\frac{64}{83}=0.7711,
\qquad w_\beta=\frac{28-9}{92-9}=\frac{19}{83}=0.2289.}
$$
Thus the equilibrium material is \b[77.1% $\alpha$ and 22.9% $\beta$ by <mass>] just below the <eutectic temperature>. These are phase fractions; converting them to <volume fractions> would require <densities>.