more preventive maintenance and may be used only $100$ hours each week. The market for all six com$-$puter components is vast, and Quitmeyer Electronics believes that it can sell as many units of each product as it can manufacture. The table that follows summa$-$rizes the revenue and material cost for each product:$$DEVICE$$Internal modem External modem$$Graphics circuit board CD drive$$Hard disk drive$$Memory expansion board$$REVENUE PER UNIT SOLD $($$$)200120180130430260$MATERIAL COST PER UNIT $($$$)3525404517060$In addition, variable labor costs are $$15$ per hour$$for test device $1,$ $$12$ per hour for test device $2,$ and $$18$ per hour for test device $3.$ Quitmeyer Electronics wants to maximize its profits. QX $($a$)$ Formulate this problem as an LP model problem. $($b$)$ Solve the problem by computer. What is the best product mix?