Linear Algebra orthogonal Sets Question

Write x as the sum of two vectors, one in span{u1,u2,u3} and one in span {u4}. You may assume that {u1,u2,u3,u4} is an orthogonal set.

U1 U2 U3 U4 x
[0] [3] [1] [5] [10]
[1] [5] [0] [-3] [-8]
[-4] [1] [1] [-1] [2]
[-1] [1] [-4] [1] [0]

Any help or ideas on how to solve this would be much appreciated. Thanks!

Normalize the vectors (divide each vector by its length) in order to convert an orthogonal set to an orthonormal set.
In other words, calculate ui* = ui / (length of ui), for 1 <= i <= 4, to form the set {u1*,u2*,u3*,u4*}, which becomes an orthonormal basis for R^4.

Note that x is in R^4. Then x is the sum of the two vectors

(x dot u1*)u1* + (x dot u2*)u2* + (x dot u3*)u3*, which is in span {u1,u2,u3}

and

(x dot u4*)u4*, which is in span {u4}.