can you solve the system of equations:
x1 + 2x3 - x4 - x5 = 0
2x1 + x2 + x3 + x4 = 0
4x1 + 3x2 - x3 + 5x4 + 2x5 = 0
that's 3 equations in 5 unknowns. assuming the equations are independent (are your 3 vectors linearly independent?), how many "free variables" will you have? how does this help you choose a basis for W?