Sums + Differences of areas, absolute values? (2 Viewers)

[Makro]

When do I use absolute values when I'm doing these questions.

EG: Find the area bounded by the curve y=9-x and the line y=5.

I think my teacher roughly mentioned it, but I've forgotten already, is there any golden rule? Or anything to know.

 

[uberturtle]

isn't area bounded by y=5 and y=9-x infinite?
no boudnaries are set :s