$(3$ points$)$ For a lead$-$tin alloy of composition $80wt\%Sn-20wt\%Pb$ at an equilibrium state at $190C.$ What phase$($s$)$ is $($are$)$ present?

$($Note: use the Fig lin last page, and close approximation is acceptable$).$

a$.$ phase

b$.$ phase

c$)$&$$ phases

d$.$&$L$ phases

$(35=15$ points$)$ Three types of cooling were performed as drawn on the isothermal transformation diagram $($on next page$)$ for a steel of eutectoid composition. Describe the possible microstructures and their $($approximate$)$ amount$/$percentage present in the steel at the