谁能帮忙解一下！！

   Consider a consumer with a steady flow of real purchases of amount sY, o<s<=1, that are made with money. The consumer chooses how often to convert bonds, which pay a constannt interest rate of i, into money, which pays no interest. If the consumer chooses an interval of x, his or her money holdings decline linearly from sYPt, after each conversion to zero at the moment of the next conversion (here P is the price level, which is assumed constant). Each conversion has a fixed real cost of C. The consumer's problem is to choose t to minimize the average cost per unit time of conversions and foregone interest.


Q1: Find the oprimal value of t.
Q2: Whart are the consumer's average real money holdings?What is the elasticity of average money holdings with respect to i? With respect to Y?


注释： 这个是关于 The Baumol-Tobin Model的。 第一问方法是F.O.C，对t求一阶导等于0， 但这个式子应该怎么列呢？？以及第二题。 各位，帮帮忙~