Aunt lucy and uncle vernon give ty some money. when they do, he has $16. they want to be fair though, so they give his sister adine, the same amount. adine had some money from before. she says, she had the same amount that uncle vernon gave her, but now she has $20. how much did aunt lucy give each child?

this was a math question in class, and i got the right answer, but was unable to explain it. any on how to explain these types of questions? ?
i'm only 11 and 6th grade is
i know my profile says otherwise, but mom told me to never put my real