Question 518560
Let 
Present age of Anton = a
Present age of Marie = m


Anton is twice as old as Marie. 
a=2m.........(1)
Eight years ago, 
Anton age = a-8
Marie age = m-8
Then, Anton was eight years younger than three times Marie's age. 
a-8=3(m-8)-8
a-8=3m-24-8
a=3m-24-8+8
a=3m-24.........(2)
Put the value of a from (1) to (2)
2m=3m-24
2m-3m=-24
-m=-24
Multiply by -1 both sides
m=24

Put the value of m in (1)
a=2m
a=2*24
a=48

Present age of Anton = a = 48 years old
Present age of Marie = m = 24 years old