For Gwen's birthday she received 27 dollars from her mom. Her dad gave her 27 more dollars. If she spent 36 dollars. How much money did she still have?
Gwen's mom gave her 27 dollars. 
Gwen's dad gave her 27 more dollars. 
That means she had 27 + 27 = 54 dollars. 
If she spent 36 dollars, that means she would have 54 - 36 = 18 dollars.