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

Sentence: 'three elephants walk up a dirt trail from the water'. Find frequency of the letter 'l'
3

Sentence: 'there is no image here to provide a caption for'. Find frequency of the letter 'o'
5

Sentence: 'traffic light in front of building with small balconies on corner windows'. Find frequency of the letter 'a'

3