Why wont this formula work in iPad version of excel?

[Victtor]

=IF(F3>=90,”A”,IF(F3>=80,”B”,IF(F3>=70,”C”,IF(F3>=60,”D”,”F”))))

Keep getting #NAME? Error

Trying to compute a letter grade score from the number grades listed in column F

Any help, even an alternate formula, would be appreciated

 

[Fluff]

Looks like you have the wrong type of quotes, they should be like
=IF(F3>=90,"A",IF(F3>=80,"B",IF(F3>=70,"C",IF(F3>=60,"D","F"))))