A complex number $z_1$ has a magnitude $|z_1|=15$ and an angle $\theta_1=209^{\circ}$.
**Express $z_1$ in rectangular form, as $z_1=a+bi$.**
*Round $a$ and $b$ to the nearest thousandth.*
$z_1 = $ [[☃ numeric-input 1]] + [[☃ numeric-input 2]] $i$