kaplan – limiting factors

P is considering whether to continue making a component or to buy it from an outside
supplier. It uses 12,000 of the components each year.
The internal manufacturing cost comprises:
$/unit
Direct materials 3.00
Direct labor 4.00
Variable overhead 1.00
Specific fixed cost 2.50
Other fixed costs 2.00
–––––
12.50
–––––
If the direct labor were not used to manufacture the component, it would be used to
increase the production of another item for which there is unlimited demand. This other
item has a contribution of $10.00 per unit but requires $8.00 of labor per unit.
What is the maximum price per component, at which buying is preferable to internal
manufacture?
A $8.00
B $10.50
C $12.50
D $15.50

Direct material 3.00
Direct labour (W1) 9.00
Variable overhead 1.00
Specific fixed cost 2.50
–––––
15.50
(W1) Relevant cost = Contribution Forgone + Direct labour = $10/2 + $4 = $9

sir i dont understand why they have divided contribution forgone by 2
your kind assistance please..