Find all invariant subspaces $W \subset \mathbb{R}^2$ of the following linear transformations $L: \mathbb{R}^3 \rightarrow \mathbb{R}^3$ :
(a) the scaling transformation $(2 x, 3 y, 4 z)^T$;
(b) the shear $(x+3 y, y, z)^T$;
(c) counterclockwise rotation by a $45^{\circ}$ angle around the $x$-axis.