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

[EX Q]: Sentence: 'a person riding a surfboard in the middle of a wave'. Find frequency of the letter 'o'
[EX A]: 3

[EX Q]: Sentence: 'a woman is looking at sheep off in a field'. Find frequency of the letter 'm'
[EX A]: 1

[EX Q]: Sentence: 'a little girl sitting in front of a white bag filled with green apples'. Find frequency of the letter 'r'
[EX A]:
3