## Linear Algebra: A Modern Introduction

$$x=3a$$
We're given $$x-a=2(x-2a)$$ Distributing scalar multiplication over vector addition on the right hand side, we get: $$x-a=2x-4a$$ By subtracting $2x-a$ from both sides, we then move all the $x$s to the left side and all the $a$s to the right: $$-x=-3a$$ Lastly, dividing both sides by $-1$ yields $$x=3a$$