The materials handling manager of a manufacturing company is trying to forecast the cost of maintenance for the company's fleet of over$-$the$-$road tractors. The manager believes that the cost of maintaining the tractors increases with their age. The following data were collected.

$\backslash$table$[[$Age $($Years$),$Yearly Maintenance Cost $($$$)],[4\mathrm{.}5,619],[4\mathrm{.}5,1049],[4\mathrm{.}5,1033],[4,495],[4,723],[4,681],[5,890],[5,1522],[5\mathrm{.}5,987],[5,1194],[0\mathrm{.}5,163],[0\mathrm{.}5,182],[6,764],[6,1373],[1,978],[1,466],[1,549]]$

a$.$ Use linear regression model to develop a relationship to forecast the yearly maintenance cost based on the age of a tractor.

b$.$ If a section has a three$-$year old tractor, what is the forecast for the annual maintenance cost?