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

[EX Q]: Sentence: 'a little boy that has a toothbrush in his mouth'. Find frequency of the letter 'r'
[EX A]: 1

[EX Q]: Sentence: 'an airplane is being towed away from the jet bridge'. Find frequency of the letter 's'
[EX A]: 1

[EX Q]: Sentence: 'a man riding a white surfboard on a wave in the ocean'. Find frequency of the letter 'f'
[EX A]:
1