Thanks for the reply Dan.
I understand areas between the x-axis and curves, but only between two x-values.
To be completely honest, I have tried simple trial and error, and using a property of definite integrals, but I've been unsuccessful.
The answer is 3, which leads me to believe I have to subtract 5, 3 and 1 from 12. I still do not understand why and it would be extremely appreciated if you could clarify it.