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

[EX Q]: Sentence: 'a group of cars and house on truck passing in a street'. Find frequency of the letter 'i'
[EX A]: 2

[EX Q]: Sentence: 'two boys are doing skateboard jumps in the street'. Find frequency of the letter 's'
[EX A]: 4

[EX Q]: Sentence: 'there is a lot of people on the train tracks'. Find frequency of the letter 'p'
[EX A]:
2