1Department of Mathematics, Comsats Institute of Information Technology, Abbottabad, Pakistan, E-mail: tausef775650@yahoo.co.in
2Department of Mathematics, Allama Iqbal Open University, Islamabad, Pakistan, E-mail: tausef775650@yahoo.co.in
*Corresponding Author:
Sultan Hussain, Department of Mathematics, Comsats Institute of Information Technology, Abbottabad, Pakistan, Tel: +92 333 9485988 Email: