How to solve for P (A' or B') (I have most of the question down)

Give an experiment such that P(A) = 0.5 P(B) = 0.4 and P(A/B) = 0.6

P(A and B) = P(A/B)P(B) = 0.24

P(A or B) = P(A) + P (B) - P (A and B) = 0.5 + 0.4 - 0.24 = 0.66

Therefore P(A' or B') = ?

I've just forgotten how to work it out. You can also double-check my process :). Thanks!

A trick you might find helpful is De Morgan's Law.

It states that:

A and B = (A or B)'
-and-
A or B = (A and B)'

So saying P(A' or B') is equivalent to saying [P(A and B)]'

And since the inverse probability of anything is 1 - P, you can simplify your answer to:
P(A' or B') = 1 - P(A and B)