P(R or S)=.64 P(R)=.38 P(S)=.52

Question

Probability Union Rule
P(R and S)=P(R)+P(S)-P(R and S)
.64=.38+.52-P(R and S)
.54=.9-P(R and S)

At this point, how do I deal with the
-P(R and S)? I know the final answer is .26, but how do I get there?

Answer 1

treat P(R and S) as a variable, suppose it is x, then your first equation becomes

P(R or S) = P(R) + P(S) - x , .... you have a typo here
.64 = .38 + .52 - x
x = .9 - .64
x = .26

P(R and S) = .26

Answer 2

Thanks