Linear Programming

Hi, I was doing the June 2008 Question 2 on linear programming recently, however when it came to plotting the graph I labelled my axis as Y axis – No of snooker cues and X axis – No of pool cues, I did the iso contribution line referred back to the answer when the line didn’t seem to make sense and realised I had don’t the labelling the wrong way round.

Is there any rule to follow when labelling the axis as I’m a bit confused about it at the moment?

Thanks