iPad App Design Question

[laurenross]

I've been hired to do the coloring/shading of line art (in Illustrator) for an iPad app but am not sure how much to charge. I'll be given the line art in jpeg form (scanned). There will be 50 images per pack of these that I do so I think I should charge by pack (per 50 images). Each individual image will take me 45min-1hour to complete. Any suggestions as to what's fair?