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: 'two elephants walking on cement next to wall'. Find frequency of the letter 'n'

Output: 5

Input: Consider Input: Sentence: 'a family sitting at a table in a restaurant looking at their phones'. Find frequency of the letter 't'
Output: 8