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

Ex Input:
Sentence: 'a woman and a child walking down a street with a kite'. Find frequency of the letter 'n'

Ex Output:
4

Ex Input:
Sentence: 'the skateboarder is jumping over a huge statue of a shoe'. Find frequency of the letter 'i'

Ex Output:
2

Ex Input:
Sentence: 'several wine glasses placed on a glass table filled with different wines'. Find frequency of the letter 'd'

Ex Output:
3