Could someone explain how to do matrix algebra?
$$4\begin{bmatrix} 1-2a \\a \end{bmatrix}=\begin{bmatrix} b \\12 \end{bmatrix}$$
I apologize for the layout, I don't know how to fix it. When I've put a comma, this signifies that it should be on the bottom.
Much appreciated.
All you have to do is solving two equations:
$$4(1-a)=b$$ $$4a=12$$
I suggest to start with the second one.