1. Maslina Darus:
School of Mathematical Sciences, Faculty of Science and Technology, University of Kebangsaan, Malaysia, Bangi 43600, Selangor Darul Ehsan, Malaysia
2. Rabha W. Ibrahim:
School of Mathematical Sciences, Faculty of Science and Technology, University of Kebangsaan, Malaysia, Bangi 43600, Selangor Darul Ehsan, Malaysia