I don't understand where those other numbers are coming from on question 4. How did they determine those?

The prompt info:

Ash borers are infecting trees throughout Michiganabout 5% are infected. When a tree is infected, the safest course of action is to cut it down. Your company has an easy test to see whether a particular tree is infected. If a tree is infected, the test will come back positive 90% of the time. Unfortunately, if the tree is not infected, it can still show a positive test 20% of the time. Use this information to answer the following two questions

I see where everything is coming from except for the last equation statement... the 0.75/[0.76+0.005]

How were those numbers found?