assigning a function (formula)

I want to have a function assigned to a cell that gives the following result:

If the value of cell B12 is 0 to 59, the result is ‘F’
If the value of cell B12 is 60 to 69, the result is ‘D’
If the value of cell B12 is 70 to 79, the result is ‘C’
If the value of cell B12 is 80 to 89, the result is ‘B’
If the value of cell B12 is 90-100, the result is ‘A’

I am having trouble figuring out how to set this up. All feedback is appreciated.

Thanks

Your formula worked perfectly. Thanks.

Scott