Estimate the service life of a boundary$-$lubricated bushing made of sintered bronze having rotary motion, when the expected maximum wear is $0\mathrm{.}2mm$ in a clean environment with sliding velocity $=15m\frac{m}{s}$ and nominal pressure $=2$MPa.

$($a$)500$ hours

$($b$)600$ hours

$($c$)700$ hours

$($d$)800$ hours