Express $(4-5i)(-5+5i)$ in the form $a+bi$, where $a$ and $b$ are integers and $i=\sqrt{-1}$ is the imaginary unit.

Why are you having a problem with this?

It is an ordinary binomial expansion that you should have been able to do 2 or 3 years prior to being introduced to imaginary numbers.

It is just the same.

Try it for yourself. :)