>>...two sons, one of whom is twice old as the other.<<
So:
x = younger son's age now
2x = older son's age now.
>>...A man's age is three times the sum of the ages
of his two sons...<<
So:
man's age now =s 3(x + 2x), which =s 3(3x) which =s 9x
>>...In four years...<<
Younger sons' age in 4 years will be x+4
Older son's age in 4 years will be 2x+4
Man's age in 4 years will be 9x+4
>>...the sum of the son's ages (in four years)...<<
So, sum of ages =s x+4 + 2x+4 =s 3x+8 <--sum of sons ages
in 4 years.
>>...will be half of their father's age.
So,
3x+8 =
(9x+4)
Solve that for x, which will be the younger son's age.
Multiply by 2 to get the older son's age.
Add them and multiply by 3 to get the man's age.
Edwin