In each case, write X as a linear combination of the orthogonal basis of the subspace U.
(a) X = [13 -20 15]T;
U = span{[l -2 3]T, [-1 1 1]T}
(b) X = [14 1 -8 5]T ;
U = span{[2 -1 0 3]T, [2 1 -2 -]T}