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

[Q]: Sentence: 'old double decker bus parked in a lot'. Find frequency of the letter 't'
[A]: 1


[Q]: Sentence: 'an commercial airline airplane flies above the clouds'. Find frequency of the letter 'n'
[A]: 3


[Q]: Sentence: 'police stand in a group on a street's sidewalk'. Find frequency of the letter 'a'
[A]:
4