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

[Q]: Sentence: 'a construction sign is displayed on a street'. Find frequency of the letter 'i'
[A]: 4


[Q]: Sentence: 'a toasted sub sandwich is next to a salad'. Find frequency of the letter 'a'
[A]: 6


[Q]: Sentence: 'a big bear walks through some grass'. Find frequency of the letter 'a'
[A]:
4