1. Department of Mathematics, Yusuf Maitama Sule University, Kano, Nigeria
2. Department of Mathematics, Kano State College of Education, Kano, Nigeria
3. Department of Mathematics Maharaj Singh College, Saharanpur, (UP), India
4. Department of Statistics, Visva-Bharti University, Santiniketan, Bolpur 731235, West Bengal, India