A String vs. Numbers?

I want to set a formula for a cell that averages the value in several cells.

In the attached screenshot, the "4.58" value is cell K5, while the total percentage cell with the "!" is K16.

When I enter "Average > K5/K16" and click the check mark, I get this error message:

"The operator “-” expects a number, date, or duration, but cell D3 contains a string" . . . or "Numbers can't be divided by zero."

I've cleared the empty cells of spaces as other people recommended, but I continually get the same error message. Please let me know what's needed to get Numbers to cooperate. Thank you.