I want to know the answer to the following question:
How many years was Ye Zhiping involved in the school overhaul?
All the background I'm provided with is that "Ye Zhiping, the principal of Sangzao Middle School in Sangzao, one of the largest in An County, has been credited with proactive action that spared the lives of all 2,323 pupils in attendance when the earthquake happened.". Is that enough to answer the question?