Answer:
Minimun transfer price = 55
Explanation:
Transfer cost = Marginal cost + Opportunity cost
There are space capacity, so there is no opportunity cost. The division will not choose between selling to this division or customer.
This means, the maginal cost will be the minimun transfer cost.
Marginal cost: cost of producing an additional unit.
This will be the variable cost, because the fixed cost are incurred already, regardless of the transfer or not.
Minimun transfer price = 55