$11\mathrm{.}21$ Give the approximate minimum temperature at which it is possible to austenitize each of the following iron$$carbon alloys during a normalizing heat treatment: $($a$)0\mathrm{.}20$ wt$\%$ C $($b$)0\mathrm{.}76$ wt$\%$ C $($c$)0\mathrm{.}95$ wt$\%$ C$.$