The Sichuan government raised the minimum wage in the province by 12.5 percent at the end of December 2007. The monthly minimum wage went up from 400 to 450 yuan, with a minimum of 4.9 yuan per hour for part-time work, effective 26 December 2007. The government also reduced the four-tier minimum wage structure to three. The top tier mandates a minimum of 650 yuan per month, or 7.1 yuan per hour. National law allows each province to set minimum wages independently, but with a floor of 450 yuan per month.
By how much did the top tier increase minimum wage in December 2007?