Helmer's Rockers manufactures two models, Standard and Premium. Weekly demand is estimated to be 120 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

If there are 600 machine-hours available per week, how many rockers of each model should Jim Helmer produce to maximize profits?

Answer:

A. 100 units of Standard and 60 units of Premium

B. 120 units of Standard and 60 units of Premium

C.120 units of Standard and 70 units of Premium

D.85 units of Standard and 60 units of Premium

Explanation: Standard (120 units 3mh) + Premium (60 units 4mh) = 600 machine-hours

I know the answer is B, but how did you get the unit?? I mean the Standard has 120 unit, Premium has 70 units and it turns to 60 units?? HOW COME, please explain more detail how to get that 60 units??