II$-$ On the following binary isomorphous phase diagram, determine

$($a$)$ The amount of liquid when an alloy with $20\%Cu$ is cooled down to $1500C.$

$($b$)$ The composition of this alloy $($giving the $\%Ni$ in each phase$)$

$($c$)$ The amount of liquid when this alloy is cooled down to $1400C.$

$($d$)$ The composition of this alloy $($giving the $\%Ni$ in each phase$)$