1. Department of Science and Humanities, College of Science and Technology, Rinchending-450, Phuentsholing, Bhutan.
2. Department of Mathematics, R.G. Baruah College, Guwahati 781025, Assam, India.
3. Department of Applied Sciences, Institute of Science and Technology, Gauhati University, Guwahati 781014, Assam, India.