Question 603784
David  be x years
Sonny = 2x

4 years ago their ages 

David = x-4
Sonny = 2x-4

2x-4=4(x-4)

2x-4 = 4x-16
4x-2x=16-4
2x=12
/2
x= 6 --- David's age
Sonny's age = 12 

Let their sum of ages be 66 after y years
6+y+12+y = 66
2y+18=66
2y=66-18
2y= 48
/2
y=24

their sum will be 66 after 24 years

CHECK

David =6 + 24= 30
Sonny = 12+24= 36

Total = 66