Numbers 1.2

This was not complicated at all. I found the IF function fairly straight forward which is kind of concerning....I hope I completed the task correctly.... Here is my IF FUNCTION formula: =IF(I4>=93,"A",IF(I4>=83,"B",IF(I4>=70,"C",IF(I4>=65,"D","F"))))
Here is the link to my Excel Spreadsheet Numbers 1.2
I actually love Excel and would love to find the time and the tasks to become a proficient user.  The problem is that I don't have the need to use Excel that often so when I do use it the learning curve starts all over again......  That makes me shy away from it.