The age difference is equal to $10-3=7$. When the age of Karl is twice the age of Ala, the age of Ala will be equal to the age difference which is $7$. Thus, it will pass $7-3 = 4$ years. 
Karl is now $10$ years old, and Ala is $3$ years old. How many years from now will Karl be twice as old as Ala? 
Options:
[a] $$5$$ 
[b] $$10$$ 
[c] $$4$$ 
[d] $$1$$ 
[e] $$3$$ 