See that \frac{z_1}{z_2}=r(\cos\theta+i\sin\theta) where r is the modulus and \theta is the argument. Your aim is then to find the theta and r.
r is obvious to find.
Consider \theta. We know that the sides z1, z2, z1-z2 forms a triangle with side lengths 3,4 and \sqrt{37} respectively (draw a...