Would be nice to mention that you already asked that question and that you received the answer explaining that if your teacher uses FreePlayer then you can only use numeric input fields and workaround the limitation with predefined set of functions.
https://mathematica.stackexchange.com/q/180690/5478
The only way to make non numeric InputFields work in .cdf is to have an enterprise Mathematica license which allows enterprise deploymen. This most likely isn't the case here.
Or to tell the teacher to open the .cdf from Mathematica rather than a FreePlayer.
