Respuesta :

If the sum of two numbers is x

Then the equation is like this:

a+b = x

Then it says one of the number is 12. Change either a or b into 12

12 + b =x

If we want to find the other number, we need the make it into the subject

b = x - 12

Hope that help.
 Y would be the other unknown number.
 
12 + Y = X

12-12+Y=X-12

Y=X-12

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