So my wife has her adult son living with us, eating food, using water, using electricity, using gas, using the washing machine etc etc etc. For this he pays $50 per week. My wife then puts $5 into the bank to cover tithing on the $50 paid by her son. I cant seem to help her understand that this is not an increase in our income, it is simply her son paying for living expenses that we have already spent on food, water, gas, electricity etc etc etc. After all, I would like to see an adult pay less than $50 for everything he uses. Any idea on how to explain it. I do have a finance/accounting background but for some reason she still argues the point.