My Son and Tithing

My son recently said to me we are not under the Old Testament, but the New Testament. Which he says you give (Tithe) whatever, as long as you give it from your heart. So while on my way to work I thought about what he said. And, this is what I am going to share with him shortly... The Old Testament tells us what to tithe (10%) the New Testament tells us "How to do it" "Cheerfully".