Like JPS said, use the code tags on this forum's software to make your code easier to read. The tags are (code)(/code) but with square brackets instead of parentheses. This is particularly important when you have a nest if-else like that, which is pretty hard to follow without indentation.
One thing that helps me a lot when working on code is to use some easy to use sample data and run that through the program in my head or on paper (if the program is too complex to keep track of mentally). Try running some sample numbers like 95, 85, 75, 65, and 15 through your program. That way, I can use my human reasoning, which is a lot more flexible than what a computer can do although not nearly as powerful, and come up with a result. If that matches what the computer is giving me, but not what I want, then I know the logic is flawed somewhere in the program.
Now that I think about it, I think you can do this without compound if statements, if you just nest the if-else statements. But that tends to lead to convoluted code. I'm guessing your teacher is introducing it to you this way with the nesting before moving on to do it with compound ifs. But it's really hard to read your code the way it's formatted.