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

[Q]: Sentence: 'this is a sign in front of a large cathedral'. Find frequency of the letter 'a'
[A]: 5


[Q]: Sentence: 'a yellow and green train on a train track in a wooded area'. Find frequency of the letter 'o'
[A]: 4


[Q]: Sentence: 'a small aircraft sits on the tarmac during the day'. Find frequency of the letter 'd'
[A]:
2