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

[Q]: Sentence: 'a commuter bus in england by a clock tower building'. Find frequency of the letter 'w'
[A]: 1

[Q]: Sentence: 'a tennis player after hitting a shot back to the other side of the court'. Find frequency of the letter 'n'
[A]: 3

[Q]: Sentence: 'a woman is holding a tennis racket on a court'. Find frequency of the letter 'u'
[A]:
1