Task 1. Martin is older than his sisters Ana, Ivana, and Elena by 8, 10, and 13 years, respectively. In one year, the sum of the ages of Martin's sisters will be 39 years more than Martin's age. How old is Martin today?
Solution. First method. Let Martin be $x$ years old today. This means his sisters are $x-8, x-10$, and $x-13$ years old today. In one year, Martin will be $x+1$ years old, and his sisters will be $x-7, x-9$, and $x-12$ years old. Therefore, $x+1+39=x-7+x-9+x-12$, from which we get $x=34$. So, Martin is 34 years old today.

Second method. Let Martin be $x$ years old today. This means his sisters are $x-8, x-10$, and $x-13$ years old today. In one year, the sum of the ages of the sisters increases by 3, while Martin's age increases by 1, so today the sum of the ages of the sisters is $39-3+1=37$ years more than Martin's age. According to this, $x-8+x-10+x-13=x+37$, from which we get $x=34$. So, Martin is 34 years old today.