Jorge is 10 and his father is 40.

If you use two-variable equations and solve, you'll find how old Jorge is, and then being able to find how old his father is.

4J - F = 0
2J - F = 20

You'd negate the bottom equation so you can have a positive F and a negative F so they cancel out. So:

4J - F = 0
-2J + F = -20

...

2J = -20, and that makes Jorge -10 years old, but because you can't be a negative age, he's just 10 years old!

And if he's 10 and his father is 40, his father is 4 times older. And in twenty years, Jorge will be 30 and his father will be 60, making his father only 2 times older.