I am trying to write a formula that will look at another cell and populate an
answer depending on what is in the other cell.

For instance: in cell D28 is either a number from 1 to 10 or the letters TBD.

I want excel to look at that cell and if the number is from 8 - 10 I want it
to populate "Successful" in cell D29

if the number in D28 is between 6 - 7.9 I want it to populuate "Needs
Improvement" in cell D29

if the number in D28 is less than 6 I want it to populate "Unsuccessful" in
cell D29

If it states TBD in cell D28 I want it to populate TBD in cell D29

I was successful in writing the formula for the range of numbers, but the
twist seems to be the TBD part.

So far my formala is like this:

=IF(D148,"Successful",IF(D146,"Needs Improvement",IF(D140,"Unsuccessful")))


Any suggestions on adding the TBD part to this formula?
Thanks