Johnson Filtration, Inc., provides maintenance service for water$-$filtration systems throughout southern Florida. Suppose that in addition to information on the number of months since the machine was serviced and whether a mechanical or an electrical repair was necessary, the managers obtained a list showing which repairperson performed the service. The revised data follow.

Repair Time Months Since

in Hours Last Service Type of Repair Repairperson

$2\mathrm{.}92$ Electrical Dave Newton

$3\mathrm{.}06$ Mechanical Dave Newton

$4\mathrm{.}78$ Electrical Bob Jones

$1\mathrm{.}73$ Mechanical Dave Newton

$2\mathrm{.}92$ Electrical Dave Newton

$4\mathrm{.}87$ Electrical Bob Jones

$4\mathrm{.}29$ Mechanical Bob Jones

$4\mathrm{.}78$ Mechanical Bob Jones

$4\mathrm{.}44$ Electrical Bob Jones

$4\mathrm{.}46$ Electrical Dave Newton

a$.$ Develop the estimated regression equation to predict the repair time given the number of months since the last maintenance service, the type of repair, and the repairperson who performed the service.