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

Input: Consider Input: Sentence: 'several zebras and a giraffe in an enclosure'. Find frequency of the letter 's'

Output: 3

Input: Consider Input: Sentence: 'a man holding a baseball bat an playing baseball'. Find frequency of the letter 'l'

Output: 6

Input: Consider Input: Sentence: 'a young woman sitting on concrete stairs using her cell phone'. Find frequency of the letter 'i'
Output: 4