If I give my brother 5 dollars, then we will have the same amount of money. If instead he gives me 25 dollars, then I'll have twice as much money as he will have. How much money does my brother currently have (in dollars)?
if you began with $80 and he bagan with $70
you gave him $5 so now both of you are on $75
he gives you $25 so now you're at $100 and he's at $50