Let F be the event for "it is a female"
Let P be the event for "it is positive"
Let N be the event for "it is negative"
Note that M is non F, and P is non N.
You're looking for P(M/N), that is to say "the probability that it is a male given that it is negative.
You know that P(M)=5/20=0.25, since there are 5 male out of 20 people.
You know that P(P/M)=0.4 since 40% of the males react positively (it's equivalent to saying that there is a probability of 40% that a man reacts positively).
Since , we can say that
We know that P(P/F)=0.7 and with the same reasoning,
These is all the information given by the text.
Now use the formula for conditional probability :
But we also know that
The law of total probability gives us this formula :
You can now calculate