$($a$)$ Develop a regression model that could be used to predict the final average in the course based on the first test grade$\mathrm{.}76($b$)$ Predict the final average of a student who madeX$-$ X$(4-9)$an $83$ on the first test.$($c$)$ Give the values of r and $7$ for this model. Inter pret the value of $?$ in the context of this problem.