Question

(4-3i)(-5+4i)
simplify

Answer 1

Have you learned FOIL?

Answer 2

First, Outer, Inner, Last

Multiply the first terms:
(4)(-5)

Outer:
(4)(4l)

Inner:
(-5)(-3l)

Last:
(-3l)(4l)

Then add up the sums

Answer 3

If those little letters are i's then

i=sqrt(-1)
i^2=-1