In this task, you need to count the number of times the given letter appears in the given sentence.

Sentence: 'pedestrian in stripe clothing standing on street corner'. Find frequency of the letter 's'
4

Sentence: 'people playing wii bowling in a modern library'. Find frequency of the letter 'o'
3

Sentence: 'a child throwing a ball towards a batter during a ballgame on a field'. Find frequency of the letter 'l'
6