No idea, that seems an odd way to price it, since lb of shirts is going to take longer than a lb of tea-towels (not that I get teatowels ironed!)
I pay £8 an hour and she's quick. Sent my entire week's worth of laundry, including all bedding and dh's shirts & it came to £16. To get a sense of scale, the previous woman who did our ironing seemed to think it was our responsibility to stop her having to claim benefits and wanted closer to £50, which was more per hour than I earn, and at that point we parted company