1. Department of Mathematics, Ministry of General Education, Anhui Xinhua University, Hefei, China
2. Department of Chemistry, COMSATS University Islamabad, Lahore Campus, Lahore, Pakistan
3. Department of Mathematics, COMSATS University Islamabad, Lahore Campus, Lahore, Pakistan
4. Department of Mathematics, Addis Ababa University, Addis Ababa, Ethiopia