Answer:
He will have to use two batteries instead of just one.
Explanation:
The way Brady could increase the strength of his electromagnet and pick up more thumbtacks is for him to increase the current. He can achieve this either by adding a second battery or by adding more coils of wire.
This is because using 2 batteries will make the amount of current in the coils to increase and this will in turn produce a higher electromagnetic field in the nail.
