Alright, lets get started.
The ages of all four sisters will be = x, x+2, x+4, x+6
As per given in question, two times of youngest sister age exceeds the oldest sister age by 30 means

Simplifying the equation



So this is the age of youngest sister.
So, age of oldest sister will be

Hene the age of oldest sister is 42 years. : Answer
Hope it will help :)