How would i go about finishing this code for these math functions to work properly in Visual Studio

public class MathFunctions { private log4net.ILog logger = log4net.LogManager.GetLogger(typeof(MathFunctions)); internal static readonly string ErrorMessage = "Error";

public string Add(string input1, string input2) { // TODO: Implement throw new NotImplementedException(); }

public string Subtract(string input1, string input2) { // TODO: Implement throw new NotImplementedException(); }

public string Multiply(string input1, string input2) { // TODO: Implement throw new NotImplementedException(); }

public string Divide(string input1, string input2) { // TODO: Implement throw new NotImplementedException(); }

public string Modulus(string input1, string input2) { // TODO: Implement throw new NotImplementedException(); }

public string Power(string input1, string input2) { // TODO: Implement throw new NotImplementedException(); }

}

}