Question 518922
Let
Present age of father = f
Present age of son = s


In five years time,
Man age = f+5
Son age = s+5
then father will be  three times as old as his son.
f+5=3(s+5)
f+5=3s+15
f=3s+15-5
f=3s+10..........(1)

Four years ago 
Man age = f-4
Son age = s-4
then father was six times as old as his son.
f-4=6(s-4)
f-4=6s-24
f=6s-24+4
f=6s-20..........(2)
Put the value of f from (1) to (2)
3s+10=6s-20
3s-6s=-10-20
-3s=-30
-3s/-3=-30/-3
s=10
Put the value of s in (1)
f=3(10)+10
f=30+10
f=40

Present age of father = f = 40 years old
Present age of son = s = 10 years old