Question 1110355
The wording you posted does not talk about the sum of the ages of the two kids.
Did you mean "ages" or "sum of the ages" of the two kids?
 
Each of the two kids will be 43 years old someday (unless one or both die at a younger age).
That would give you two different equations,
{{{9+x=43}}} and {{{9+x=43}}} , with two different results.
Of course, at no time will the father and a child be the same age.
 
The sum of the ages of the two kids will always be an even number,
so the sum will never be 43.
However, as all 3 of them age by {{{x}}} years,
the sum of the two children's ages will be the age of the father when
{{{9 + x + 11 + x = 43 + x}}} .
That may be the intended problem and equation.