You may want to review multiplying complex numbers first.
Dividing complex numbers requires a trick. Suppose you need to divide (5 − 2i) / (−1 − 4i). You multiply the numerator and the denominator both by −1 + 4i. This is called the conjugate of the denominator; in general, the conjugate of a complex number is what you get when you switch the sign in the middle. This gives you 3 + 22i in the numerator, but 17 in the denominator. Now, the denominator's a real number, so we can divide; just divide each term of the (new) numerator by 17. So the answer is 3 ⁄ 17 + 22 ⁄ 17 * i. This always works, since the product of a number and its conjugate is always real.
If the denominator is just something times i, then its conjugate is just its additive inverse; so the conjugate of 2i is −2i.