PLEASE HELP (COMP. SCI 1)

As a coder at a pharmaceutical company, you've been tasked with writing a program that will determine how long a particular drug may stay on shelves to be sold in stores. Assume this drug loses 12% of its effectiveness every month (save into a variable, but you don't have to get this value from the keyboard), and must be discarded when effectiveness dips below 50%. Write a program that prints how many months the drug can remain on shelves.