1. Department of Mathematics, SRKR Engineering College, Bhimavaram 534 204, A.P., India
2. Department of Mathematics, Acharya Nagarjuna University, Nagarjuna Nagar 522 510, A.P., India
3. Department of Mathematics, Lingayas Institute of Management and Technology, Madalavarigudem 521212, Krishna Dt., A.P., India
4. Department of Mathematics, College of Natural and Computational Sciences, Wollega University, East Wollega, Nekemte, Ethiopia