Answer:
$6.63
Step-by-step explanation:
As Division B has spare capacity after fullfillling their outside consumer demand It can provide to Division A at their marginal cost to make a better use of the fixed cost.
In this case, Division B can sale up to 10,600 lamps which is the amount needed for DIvision A.
The sales variable cost are not considered as the division will assume any when selling internally.