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

[EX Q]: Sentence: 'a crowd of people skiing and enjoying the snow'. Find frequency of the letter 'o'
[EX A]: 5

[EX Q]: Sentence: 'a young boy bouncing a tennis ball on a tennis racquet'. Find frequency of the letter 'a'
[EX A]: 5

[EX Q]: Sentence: 'a young girl flies a kite in a city'. Find frequency of the letter 'u'
[EX A]:
1