Your brother is now 11. If your brother is 3, you put '8+x'=x+5 to get your cousins age. Once you have x+5, set it equal to 2(x-3) and solve that. You should get x+5=2x-6 and you get x=11. You add 8 to get your cousins age. So your brother is 11 and your cousin is 19.