A company implements Fixed-Period model and it has analyzed and studied the sales of a commodity. Found that the user needs obey to the normal distribution, the past 8 months purchase quantities were: 23、27、25、31、29、33、37、35 (ton / month), the lead time is a month, an order cost is 150 yuan, 1 ton of goods storing a month cost 10 yuan. Please determine the order strategy according to the above conditions. If the company sets up a maximum inventory of 100 tons, the first order inspection found that the existing stock were 52 tons, 7 tons had been placed but not arrived, 4 tons had been sold but not picked. Try to calculate the first order quantity.