$(20\text{'})$ Consider $Q_2||$ prmp $|C_{\text{m}\text{a}\text{x}}|$ with the jobs under the Longest Remaining Processing Time first $($LRPT$)$ schedule.

$[$ jobs $,1,2,3,4],[p_j,36,24,16,12]$

and machine speeds $v_l=2$ and $v_2=1.$

$($a$)$ Find the makespan under LRPT when preemptions can only be made at the time points $0,4,8,12,$ and so on$.(5\text{'})$

$($b$)$ Find the makespan under LRPT when preemptions can only be made at the time points $0,2,4,6,8,10,12,$ and so on$.(5\text{'})$

$($c$)$ Find the makespan under LRPT when preemptions can be made at any time. $(5\text{'})$

$($d$)$ Compare the makespans under $($a$),($b$),$ and $($c$).(5\text{'})$