Answer:
a. Break even in unit sales = $960,000 / $12,000 - $9,000 = $960,000 / $3,000 = 320
b. Margin of safety = ($12,000*400) - ($12,000*320) = $4800000 - $3840000 = $960,000
c. Degree of operating leverage = Contribution / PBIT
Contribution = ($12,000*400) - ($9,000*320) = 4800000 - 2880000 = 1920000
PBIT = 1920000/960,000 = 2
Degree of operating leverage = 1920000/2
Degree of operating leverage = 960,000