7. Let $S, T: \mathbb{R}^3 \to \mathbb{R}^4$ be linear transformations such that $T(1, 2, 3) = (1, 1, 0, -1)$ and $S(1, 2, 3) = (2, -1, 2, 2)$. Compute $(3T - 2S)(1, 2, 3)$.
8. Compute $(T + 2S)(x_1, x_2, x_3, x_4)$, where
$T(x_1, x_2, x_3, x_4) = (x_1 - x_2 + x_3, x_1 - x_2 + 2x_3 - x_4)$,
$S(x_1, x_2, x_3, x_4) = (x_2 - x_3 + 2x_4, x_1 + x_3 - x_4)$.
