Row Reduction & Rank · Easy problem

To solve $A\mathbf x = \mathbf b$ with $A = LU$, first solve $L\mathbf c = \mathbf b$. If $L = \begin{pmatrix} 1 & 0 \\ 2 & 1 \end{pmatrix}$ and $\mathbf b = \begin{pmatrix} 3 \\ 10 \end{pmatrix}$, what is $c_2$?