1. General Education Department, Anhui Xinhua University, Hefei 230088, China
2. Department of Mathematics, Lahore Campus, COMSATS University Islamabad, Lahore 54000, Pakistan
3. Department of Mathematics, Quaid e Azam University, Islamabad 45320, Pakistan
4. Faculty of Chemistry and Technology, University of Split, Rudera Boškovića 35, 21000 Split, Croatia