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

[Q]: Sentence: 'a bathroom with a sink, counter top, and mirror is shown'. Find frequency of the letter 'i'
[A]: 4


[Q]: Sentence: 'a white police vehicle parked on a paved street'. Find frequency of the letter 'a'
[A]: 4


[Q]: Sentence: 'a man flying through the air while riding a snowboard'. Find frequency of the letter 'n'
[A]:
4