why is it A) the correct answer and not B)?

Helmer's Rockers manufactures two models of trumpets, Standard and Premium. This week's demand is estimated to be 100 units of the Standard Model and 70 units of the Premium Model. The following per unit data apply: Standard Premium Contribution margin per unit 18 20 Number of machine-hours required 3 4 40. If there are 600 machine-hours available per wedc, how many trumpets of each model should Helmet produce to maximize this week's prot? A) 100 units of Standard and 70 units of Premium B) 100 units of Standard and 75 units of Premium C) 85 units of Standard and 60 units of Premium D) 72 units of Standard and 70 units of Premium