HELP ASAP!! Which letter is the spinner least likely to land on?

The spinner is least likely to land on
Blank 1:

The answer is c becuse there’s only 2 cs and 3 of the others

I am not positive i did this a while ago but i think you subtract r^2 on both sides getting 18r+73=-9(r^2)
Then you can divide 18 from 18r getting r+73=-9(r^2) (divided by symbol) 18
Then you subtract 73 and u get R=-9(r^2)
+73
18

Sorry if thats totally wrong but thats all I remember