There were 3 dollars in Olivia's wallet. She collected 49 more dollars from an atm. After she visited a supermarket there were 49 dollars left. How much more money did she collect at the atm than she spent at the supermarket?
Olivia had 3 dollars in her wallet. 
She went to the ATM and collected 49 more dollars. 
She went to the supermarket and spent some amount of money. 
She now has 49 dollars left. 

So we want to know how much money she spent at the supermarket. 

Olivia had 3 dollars in her wallet to start. 
She collected 49 more dollars from the ATM, so she had 52 dollars in total. 
She spent some amount of money at the supermarket, and now she has 49 dollars left. 

How much money did she spend at the supermarket? 

3 + 49 = 52
52 - 49 = 3

Olivia spent 3 dollars at the supermarket.