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

[Q]: Sentence: 'some people sitting on surfboards in the water'. Find frequency of the letter 't'
[A]: 4


[Q]: Sentence: 'a number of small boats on a beach near an umbrella'. Find frequency of the letter 's'
[A]: 2


[Q]: Sentence: 'a blue and white hospital room with three beds'. Find frequency of the letter 'a'
[A]:
3