$1.$ The bottom$-$line results for the three plans are: Bill's plan $$49,380,240$ Sandra's plan $548,972,440$ No Promotion S$47,664,204$ Slightly different results can be obtained if all decision variables are declared as integers.

$2.$ Both plans suffer from the additional discount; Bill's plan on a percentage basis is a slightly larger decline than Sandy's.

Bill's plan $$46,969,480-$ a decline of $$2\mathrm{.}4$ million

Sandra's plan $$46,867,040-$ a decline of $$2\mathrm{.}1$ million

From a production floor perspective, Bill's plan switches to a virtually level labor force with a shortfall of $40$ units made up by subcontracting in the last month. Sandra's plan also features greater labor stability with far less subcontracting until December, when $200$ units are subcontracted.

$3.$ Sandra's plan rings up $$48,903,800$ by laying off $43$ workers in July, hiring $75$ in November and another $3$ in December, and subcontracting $200$ units in December.

Bill's plan results in a profit of S$49,966,611$ and has significant fluctuations in the labor pool; $174$ workers are laid off in July, $103$ and $206$ are hired back in September and October respectively. Overtime production exceeds subcontracting production throughout the planning period.