Because when grandma died, Lin Li was 2/5 of her father's age, and according to the conditions in the question, her father was 30 years older than Li Lin.

Well, fathers who are 30 years older than Li Lin should account for another 3/5, which means 30/0.6=50 years old.

Lin Li's age this year should be 30/0.6-30=20. Grandma's death age should be 20+50=70.

If calculated by equation, then

Suppose my grandmother died at the age of X, then

X=30/0.6+(30/0.6-30)=70