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

[Q]: Sentence: 'a young elephant is touching a bigger elephant with its trunk'. Find frequency of the letter 'i'
[A]: 5

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

[Q]: Sentence: 'a catcher playing baseball in the snow beside a snowman'. Find frequency of the letter 'a'
[A]:
7