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AS Physics question - help please!

I'm sure this should be simple but I just can't seem to get it... any help would be much appreciated.

A shallow trough has the shape shown in the diagram (see attachment, sorry for bad quality!) and contains a liquid with positive and negative ions. Electrodes are fixed to the ends of the trough at A and D and connected to a battery. The width of the trough at A is twice the width of the trough at D.

Using I = nAvq, v is inversely proportional to A when the other variables stay the same, as they would, right? In one part of the question I worked out that the ions move twice as fast between C and D as between A and B. Is that correct?

Part of the q I'm majorly stuck on...

"Draw a graph of current against distance from A, to show how the average speed of the positive ions varies along the line ABCD".

I don't get how I can show the average speed by plotting this :confused: