Hello MHF, would appreciate some help with the following equestions;

Determine which of the following sets are subspaces. Give reasons for your answers.

(a)$\displaystyle H=\left\{\left[\begin{array}{cc}s\\2s\\0\end{array}\right]:s\in\mathbb{R},s\geq0 \right\}$

(b)$\displaystyle L=\left\{\left[\begin{array}{cc}s+2t+1\\s+3t\end{array}\right]:s,t\in\mathbb{R} \right\}$