Consider the $Cu-Al$ phase diagram, where the horizontal axis represents the composition of copper $($in weight percent$)$ and the vertical axis represents temperature:

a$.$ Determine the composition of the alloy at the eutectic point.

b$.$ Describe the phases present and their compositions at a temperature of $750C$ for an alloy with $30\%Cu.$

c$.$ Explain the significance of the peritectic reaction in the context of alloy solidification.