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

[EX Q]: Sentence: 'a little boy that has a toothbrush in his mouth'. Find frequency of the letter 'r'
[EX A]: 1

[EX Q]: Sentence: 'a man in costume talking on a cell phone'. Find frequency of the letter 'm'
[EX A]: 2

[EX Q]: Sentence: 'roast meat arranged on a plate with vegetables'. Find frequency of the letter 'l'
[EX A]:
2