Let the fraction be x/y.
We know that x + y = 12, and that (x) / (y + 3) = 12.
Multiplying both sides of the second equation by (y + 3), we get:
x = 12(y + 3)
Substituting this into the first equation, we get:
12(y + 3) + y = 12
Expanding and simplifying, we get:
13y + 36 = 12
Subtracting 36 from both sides, we get:
13y = -24
Dividing both sides by 13, we get:
y = -24/13
Substituting this value of y into the equation x + y = 12, we get:
x - 24/13 = 12
Multiplying both sides by 13, we get:
13x - 24 = 156
Adding 24 to both sides, we get:
13x = 180
Dividing both sides by 13, we get:
x = 180/13
Therefore, the fraction is 180/13 divided by -24/13, which simplifies to -15/2.