Answer:
$20
Explanation:
Broker's usually take a percentage of the money made or a fixed amount no matter how much is traded.
Here, the broker charges $10 per trade. So, it doesn't matter how much you do trade, the broker will charge $10 PER TRANSACTION.
Samantha bought stocks worth 2500 (1 transaction)
Samantha sold these again for 2750 (1 transaction).
So there were 2 trades made by Samantha.
So broker would charge $10 + $10 = $20