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

Input: Consider Input: Sentence: 'a airplane view of a big factory some people and cars'. Find frequency of the letter 'f'

Output: 2

Input: Consider Input: Sentence: 'a woman walking on a shore next to a river'. Find frequency of the letter 'v'

Output: 1

Input: Consider Input: Sentence: 'a cat sitting on a laptop keyboard on a desk'. Find frequency of the letter 'n'
Output: 3