(-6 - 5i)(1 - 3i)
you foil this like you would any other set of binomials, so you'll multiply negative 6 and 1, then -5i and 1, etc:
-6 - 5i + 9i - 15
5i and 3i simplify to -15 because 5*3 is 15, and i*i = -1
then you just add like terms:
-21 - 5i + 9i
-21 + 4i is your answer.