Step-by-step explanation:
(b) If
then
Note that
cancel out so we get

Solving for
we get

(c) I'm not sure what the problem is asking for but here goes. As r doubles,
becomes

I believe 30 is the answer :)
So uhh I’m so sorry to tell you but I don’t know how to do math myself and I just need points so I’m answering this.. but I’m sure If you just cheat off a smart person in your class you’ll be fine. If you need any tips on how to cheat lmk I’ll gladly help