Now

Ethan : Aunt = 1 : 3 = 3 : 9 (difference = 6)

10 years ago

Ethan : Aunt = 1 : 7 (difference remains unchanged = 6)

3u – 1u = 10

1u = 5

Ethan is now 3u = 15 years old

Method 1 :
Ethan : 1u + 10
His aunt : 7u + 10

7u + 10 ——- (1u + 10) x 3 = 3u + 30
1u ——- (30 – 10)/(7 – 3) = 5
5 + 10 = 15

Method 2 :
Ethan :
1u – 10 ——- 1p
7u – 70 ——- 7p

His aunt :
3u – 10 ——- 7p
7u – 70 ——- 3u – 10

7u – 3u = 4u ——- 70 – 10 = 60
1u ——- 15

Ans : 15 years old.