The question is as follows:
Is the set of all vectors $x = [x_1, x_2, x_3, x_4]^T$ that are linear combinations of $[4, 2, 0, 1]^T$ and $[6, 3, -1, 2]^T$ and in addition satisfy the equation $x_1 = 2x_2$ a subspace of $\mathbb{R}^4$?
Could someone give me some hints on where to start with this problem?