Age??

let x be the father's age and S be the sum of ages of his five children.

acc to question

x=S..(i)

after 15 years, the father'sa ge will be x+15

each of the child's age aso will increase by 15 in 15 years, so the sum of their ages will increase by 5(15)=75 years

 so after 15 years, the sum of their ages will be S+15

acc to question,

2(x+15)=S+15..(ii)

solving (i) and (ii) we get,

S=45

x=45