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

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


[Q]: Sentence: 'the little girl is flying her kite in the field'. Find frequency of the letter 'i'
[A]: 7


[Q]: Sentence: 'a cat is curious about a neoprene water bottle'. Find frequency of the letter 'b'
[A]:
2