$4-26.$ Consider the Strollers$-$to$-$Go production problem $($Problem $4-24).$

$($a$)$ Suppose that Strollers$-$to$-$Go could purchase additional fabrication time at a cost of $$10\mathrm{.}50$ per hour. Should it be interested? Why or why not? What is the most that it would be willing to pay for an additional hour of fabrication time?

$($b$)$ Suppose that Strollers$-$to$-$Go could purchase fabrication time only in multiples of $40-$hour bundles. How many bundles should it be willing to purchase then?