The rate is 12 per carton.
y=2x-3
2 is the slope (movement of the line) and it will increase or decrease with the variable and -3 is your starting point so it stay the same
I think the greatest possible error that may occur in this kind of question is how this measurements are measured and the units is either correct or not. The factor that you should consider in a measurement is first the accuracy, second is the unit and third is the correct conversion.