If Sebastian is 40 years old and 10 years older than his sister, his sister is 40-10=<<40-10=30>>30 years old.
Five years ago, Sebastian was 40-5=<<40-5=35>>35 years old.
Similarly, Sebastian's sister's age was 30-5=<<30-5=25>>25 years old.
The sum of their ages five years ago was 25+35=<<25+35=60>>60
Five years ago, the sum of Sebastian's age and his sister's age was 3/4 of their father's age, meaning their father's age was 60 / 3/4 = 80 years.
The father's age is now 80+5=<<80+5=85>>85
#### 85