Question 236806
Since dad is 20 years older than his son, dad must be twice as old in order for his son to be half his age.
At this point dad will be 40 and son 20.  Does that make sense?
.
Now, since the problem brings you back 10 years from Dad being twice Son's age, you need to deduct 10 years from Dad and Son to find their current ages.
.
I'll let you finish it now.