[د.امير]

you need to solve Schrodinger equation for a particle in a box,
read here for background and solution starts from page 21 for <p> and <P2>
http://www.unige.ch/sciences/chifi/g...ture07_umn.pdf
for solution to <x> and <x2> see here
http://www.unige.ch/sciences/chifi/g..._sept28_CC.pdf
the integration above from 0 to L, in your case is 0 to a, so remember that.
good luck