We can pose this question as follows:
1. We have that Billy is 4 years older than Johnny:
B = J + 4
2. Sally is twice as old as Johnny:
S = 2J
3. The sum of their ages is 32, we have:
B + S + J = 32.
Then, we have that:
J + 4 + 2J + J = 32 (we substitute the previous values of the equations above).
Summing the like terms, we can find the value of J:
4J + 4 = 32 ---> 4J = 32 - 4 ---> J = 28/4 ---> J = 7.
Then, Johnny is 7 years old.
Sally is:
S = 2 * J ---> S = 2 * 7 ---> S = 14 years old.
And Billy is:
B = J + 4 ---> B = 7 + 4 ---> B = 11 years old.