1. Department of Mathematical Sciences, Delaware State University, Dover DE 19901-2277, USA
2. Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia
3. School of Mathematics, Centre for Differential Equations, Continuum Mechanics and Applications, University of the Witwatersrand, Johannesburg, Wits 2050, South Africa
4. Department of Mathematics, Kuztown University of Pennsylvania, 15200 Kutztown Road, Kuztown PA 19530, USA
5. Department of Mathematics and Statistics, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia