If I give my brother $5$ dollars, then we will have the same amount of money. If instead he gives me $10$ dollars, then I'll have twice as much money as he will have. How much money does my brother currently have (in dollars)?
b = brother's money y = your money
y-5 = b + 5 Given re-arrange to y = b + 10
y+10 = 2 ( b-10) Given Sub in y = b+10
(b+10) + 10 = 2b -20
b+20 = 2b -20
b = 40 dollars y = 50 dollars