So you would want to add Lisa's amount with Kelly's amount to get how much they have together.
23.20 + 15.05 = 38.25
Then you take the amount of money Lisa and Kelly has together and subtract it from the total amount of money all three of them have together to get Maria's amount.
56.70 - 38.25 = 18.45
Maria has $18.45.
Check:
Add all three of there money amounts together and if you get $56.70 you got the right answer.
