1. Department of Mathematical Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia (UKM), 43600 Bangi Selangor, Malaysia
2. Department of Mathematics, College of Sciences and Arts, Najran University, POB 1988, Najran 11001, Saudi Arabia
3. Department of Mathematics, Faculty of Applied Science, Taiz University, Taiz, Yemen
4. Department of Mathematics, Faculty of Science, Yarmouk University, 211-63 Irbid, Jordan