1. Department of Mathematics, Faculty of Physical Sciences, Ahmadu Bello University, Zaria, Nigeria
2. Department of Mathematics, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia
3. College of Science and Arts at Khulis, Department of Mathematics, University of Jeddah, Jeddah, Saudi Arabia
4. Academy of Engineering and Medical Sciences, Department of Mathematics, Khartoum, Sudan
5. Faculty of Science, Department of Mathematics, Ain Shams University, Cairo, Egypt