(); }privatedecimalFindPayRate(){ QuantityInteger =int.Parse(textNumberPiece.Text);switch(QuantityInteger) {caseQuantityInteger >=600: PayDecimal = piece_rate_600;break;case400>=599: PayDecimal = piece_rate_599;break;case200>=399: PayDecimal = piece_rate_399;break;case1>=199: PayDecimal...