There were w dollars in Olivia's wallet. She collected x more dollars from an atm. After she visited a supermarket there were x dollars left. How much more money did she collect at the atm than she spent at the supermarket?
Olivia started with w dollars in her wallet. 

x more dollars were collected from an ATM machine. 

This means that Olivia had w + x dollars in her wallet after collecting money from the ATM machine.

After visiting the supermarket, Olivia had x dollars left in her wallet. 

This means that Olivia spent w + x - x = w dollars at the supermarket. 

Therefore, Olivia collected w + x - w = x more dollars at the ATM machine than she spent at the supermarket.