1. Department of Mathematics and Statistics, University of Swat, Swat, Khyber Pakhtunkhwa, Pakistan
2. Department of Mathematics and Sciences, Prince Sultan University, P. O. Box 66833, Riyadh 11586, Saudi Arabia
3. Department of Mathematics, University of Malakand, Dir(L), P. O. Box 18000, Chakdara, KPK, Pakistan
4. College of Engineering and Technology, American University of the Middle East, Kuwait