Okay, let’s tackle this. So Lieng Sary has 31 years of experience, which is extremely long for a mathematician. Her experience is in teaching, which is not typically in high demand or high pay. Location is Cambodia, which is a developing country with a lower cost of living. Considering her extensive experience, I would expect a higher rate. However, given the teaching context, I'll estimate a lower rate. Maybe around $50 per hour, considering the low cost of living in Cambodia and the fact that she's been working for 31 years. This rate is lower than what I would expect for someone with her experience in a developed country, but it's still a reasonable estimate given the context.