1. School of Mathematics, Statistics and Computer Science, University of KwaZulu-Natal, Durban, South Africa
2. DSI-NRF Center of Excellence in Mathematical and Statistical Sciences (CoE-MaSS), South Africa
3. Department of Computer Science and Mathematics, Mountain Top University, Prayer City, Ogun State, Nigeria
4. Department of Mathematics, Usmanu Danfodiyo University Sokoto, PMB 2364, Sokoto State, Nigeria
5. Department of Mathematics and Applied Mathematics, Sefako Makgatho Health Sciences University, P. O. Box 94, Medunsa 0204, Ga-Rankuwa, South Africa