Excel: IF then question

Hello,

I've got 2 questions. First one is I have an if statement look like this but something is wrong:

=IF(C31>400), C31*0.8, C31*0.9

And it's not going through because of invalid format.


Second question is this:

Number of Bags sold per day-- The number of bags sold per day is inversely proportional to how much marketing you do (variables are: Low, Medium, High). If you choose a Low amount of marketing, the number of bags sold per day will be the total market for bags (C29)/5. If you choose Medium amount of maketing, C29/3, high=c29/2.

Using the INT function how in the world do I do this???

I do know to start with =INT(
:D

You'll save my butt with this. I have another 3 hours worth of work ahead of me on this excel sheet and I need to get past this first lol