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

Input: Consider Input: Sentence: 'a silver train crossing the road on tracks'. Find frequency of the letter 'r'

Output: 5

Input: Consider Input: Sentence: 'a group of people standing around a table filled with assorted electronic devices'. Find frequency of the letter 'w'

Output: 1

Input: Consider Input: Sentence: 'a person and surf board handling a wave'. Find frequency of the letter 'a'
Output: 6