We thank anonymous referees and Professor J. Wiegerinck for helping us simplify the proof of Theorems 1 and 4, respectively. This research was partly supported by the Hunan Provincial Education Department Outstanding Youth Project (No. 18B365), the Science and Technology Plan Project of Hengyang City, People's Republic of China (No. 2018 kJ125), the Science and Technology Plan Project of Hunan Province, People's Republic of China (No. 2016TP1020), the Science and Technology Plan Project of Hengyang City, People's Republic of China (No. 2017 kJ183), the Application-Oriented Characterized Disciplines, Double First-Class University Project of Hunan Province, People's Republic of China (Xiangjiaotong [2018]469), and the Open Fund Project of Hunan Provincial Key Laboratory of Intelligent Information Processing and Application for Hengyang Normal University, People's Republic of China (No. IIPA18K06). The work of the second author is supported in part by Mathematical Research Impact Centric Support (MATRICS) grant, File No.: MTR/2017/000367, by the Science and Engineering Research Board (SERB), Department of Science and Technology (DST), Government of India.