work done = 0 as isochoric process.
So. Q = ΔU = nCvΔT
==> 10000*4.2 = (106*10*10-3/R*300)*(3R/2).ΔT
==> ΔT = 840
==> Tfinal = 300+840 = 1140 K
:( no one noticed for such a long time that i had written 10000 cal as 10000/4.2 J instead of 10000*4.2 J