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: 'a woman standing in front of a bathroom sink in front of a mirror'. Find frequency of the letter 'o'
8

Sentence: 'a green line of train cars being pulled along the tracks'. Find frequency of the letter 'o'

2