1. Department of Mathematics, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia
2. Department of Mathematics and Applied Mathematics, University of Pretoria, Lynnwood Road, Pretoria 0002, South Africa
3. Institute of Research and Development of Process (IIDP), Faculty of Science and Technology, University of the Basque Country, 48940 Leioa, Spain
4. Department of Mathematics, COMSATS Institute of Information Technology, Abbottabad 22060, Pakistan