1. University of Jeddah, College of Science and Arts at Khulis, Department of Mathematics, Jeddah, Saudi Arabia
2. Department of Mathematics, Faculty of Science, Ain Shams University, Cairo, Egypt
3. Department of Mathematics, Faculty of Education, Alzaiem Alazhari University, Khartoum, Sudan
4. Academy of Engineering and Medical Sciences, Department of Mathematics, Khartoum, Sudan