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

[EX Q]: Sentence: 'small airplane in the process of taking off'. Find frequency of the letter 'e'
[EX A]: 3

[EX Q]: Sentence: 'tow birds flying by a long necked crane'. Find frequency of the letter 'f'
[EX A]: 1

[EX Q]: Sentence: 'several cars are driving down a busy street'. Find frequency of the letter 'r'
[EX A]:
5