Tourist visa extension notice

I just renewed a L type one (in Shijiazhuang, Hebei) and was required to submit a document proving $ in the bank. The requirement was 21,000rmb (~USD100/day) for a 30 day extension. A photocopy of a stamped balance inquiry from Bank of China did the trick. I was advised that I could apply for two extensions, but that two would not be granted at the same PSB office.