Answer:
A. 11 %
Step-by-step explanation:
Given that TopCo owns 40% of Botco, in order to gain control botco, it must either directly or/and indirectly have more than 50% of botco voting stock. Meaning it must acquire more than 10% extra in order to gain control. Thus, if Midco that topco have 60% of is able to acquire 11% of Botco, then topco will be able to have 51% control over botco with 40% coming directly and 11% coming indirectly through it 60% control over Midco.