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

Input: Consider Input: Sentence: 'there is a baseball game on and a few people are watching'. Find frequency of the letter 'i'

Output: 2

Input: Consider Input: Sentence: 'a woman sitting in front of a giant slice of cheese pizza'. Find frequency of the letter 'e'

Output: 4

Input: Consider Input: Sentence: 'a black and white photo of a woman on her mobile phone'. Find frequency of the letter 'o'
Output: 7