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

[EX Q]: Sentence: 'a river with a long dragon boat in it and rowers on the boat in sets of two, along with two other people'. Find frequency of the letter 'h'
[EX A]: 4

[EX Q]: Sentence: 'several zebras  and a giraffe in an enclosure'. Find frequency of the letter 's'
[EX A]: 3

[EX Q]: Sentence: 'a train engine and several cars moving along a track in a city'. Find frequency of the letter 'a'
[EX A]:
9