Billy is 44, which is twice as old as Nina was x years ago, which was N-x
44 = 2(N-x)
x years ago, Billy, who is now 44, was 44-x, which is as old as Nina is now, N.
44-x = N
The system of equations is
44 = 2(N-x)
44-x = N
Solve that system by substitution and get x = 11, N = 33
Nina is 33.
Checking: 11 years ago Billy was 44-11=33, which is Nina's present
age, and Nina was 33-11=22. So Billy, at 44, is now twice as old as
Nina was 11 years ago at age 22.
Edwin
