Hello, I need help with Scheme programming.

I am trying to write a program that will output how many times the letter (O) was in the string.

for example, if the string is "Scheme is cool". the output will be like: O appears 2 times.

I'm super new in this language so does not have much knowledge. after googling I know there is a function call "string-contains?".

also, I find out example with that function: (string-contains? "Racket" "ack") in racket guide. But, when I tried to run it in racket output, is false even though it is true.

so I am kinda lost need help on how to write a program that will output how many times letter (O) appeared in the string.

Thank you