Mmsee

#1
If I am given a random vector X with mean [0 1 -1 2]'
and a covariance matrix C= [.1 -.3 .5 .1 ; -.3 1 .1 .2; .5 .1 2 .3 ; .1 .2 .3 .2]
how do I find the MMSEE of x1 given x2 = 0 x3 = 0 x4 = 0