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

Example Input: Sentence: 'people plating cake in an office meeting room'. Find frequency of the letter 'g'
Example Output: 2

Example Input: Sentence: 'there is a stop sign that has a reflection in a puddle'. Find frequency of the letter 'e'
Example Output: 5

Example Input: Sentence: 'large orange colored train riding down tracks near a much older model train'. Find frequency of the letter 'e'
Example Output:
6