Question

How do i solve this complex number (-3i)(-5i)(6+i)

Answer 1

First combine the 3i and 5i. They are multiplied.
3*5 * i*i
i*i = - 1
3*5 = 15
This much is - 15

Now use the distributive law.
-15 * (6 + i)
-90 - 15i