1. Department of Mathematics, College of Physical and Applied Sciences, Michael Okpara University of Agriculture, Umudike, Umuahia P.O. Box 7267, Abia State, Nigeria
2. Functional Analysis and Optimization Research Group Laboratory (FANORG), Department of Mathematics, School of Physical Sciences, Federal University of Technology, Owerri, Owerri P.O. Box 1526, Imo State, Nigeria
3. Department of Mathematics and Statistics, North Carolina A&T State University, Greensboro, NC 27411, USA