Example $4\mathrm{.}4.$ Determine $a_0$ and $a_1$ in the equation $y=a_0+a_{1}x$ to provide a best fit in the sense of least$-$squares deviation to the data points $(1,4\mathrm{.}9),(3,11\mathrm{.}2),(4,13\mathrm{.}7),$ and $(6,20\mathrm{.}1).$