$(15$ pts$)$ A hypothetical A$-$B alloy of composition $60wt\%$ B $-40wt\%A$ at some temperature is

found to consist of mass fractions of $0\mathrm{.}3$ for $$ and $0\mathrm{.}7$ for $$ phases. If the composition of the $$ phase is

$80wt\%$ B$-20$ wt$\%$ A$,$ what is the composition of the $$ phase?