Matrices and Linear Systems

Homework Statement

Write the given system in the form $$x'=P(t)x + f(t)$$

$$x'=-3y , y'=3x$$

Homework Equations

$$x'=P(t)x + f(t)$$
$$x(t)=c_1x_1(t)+c_2x_2(t)+...+c_nx_n(t)$$

The Attempt at a Solution

I have no idea how to start this since my teacher never covered this in our notes and the book doesn't give an example of this type of problem. Please help!