Let
a-------> one of the numbers
b------> the other number
we know that
\(a+b=x\) ----> equation A
\(a=12\)
substitute the value of a in the equation A
\(12+b=x\)
solve for b
Subtract \(12\) from both sides
\(12+b-12=x-12\)
\(b=x-12\)
therefore
the answer is
The other number is \(x-12\)
