Which of these activities are you most likely to do in el banco?
1) llenar el tanque
2) echar una carta
3) cobrar un cheque
4) ir a pie

It's a vocabulary question, so what you need to do is to know what the vocabulary means: 
 el banco  is the bank 

1) llenar el tanque - fill the tank   ( you would go to a gas station for that)

2) echar una carta  - send a letter (you would go to a post office for that)

3) cobrar un cheque - collect a check, yes, you would go to el banco, this is the correct answer!

4) ir a pie - go on foot. It's not necessary to go to a bank to do that!

Can you give me the link also to the question