write the following class .Also provide a test file for the class(use separate compilation) Statistic class interface: Void add(double elem) //adds a number to the current sum Void add(double elem,int count) // add a number count times Double avg() //return the average of numbers Double stdev() //return the standers deviation Provide other member function as needed. Overload the operator<<and operator>> to read and write the statistic variable. The operator <<will print both the average and standard deviation to an output stream. The operator >> will read on element from the input stream. I don't know how can I solve this kind of problem?