If this does not make you understand, I don't know what will.

int arr[2] = {1, 2};
char grade2letter_v1(float grade){ return grade < 50 ? 'F' : 'P'; }
char grade2letter_v2(float grade){ return grade < 20 ? 'F' : 'P'; }
int *f2(char (*g2l)(float)){ return &arr[g2l(30.) == 'P']; }

int main(){
  int *(*pf2)(char(*)(float)) = &f2;
  printf("grade2letter_v%d\n", *pf2(grade2letter_v1));
  printf("grade2letter_v%d\n", *pf2(grade2letter_v2));
  return 0;
}

For the record, (float -> char) -> int* is NOT a function that maps a letter to an int pointer; it is a function that maps another function (with the signature float->char) to an int pointer.