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

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

Ex Output:
2

Ex Input:
Sentence: 'a young girl is brushing her teeth in this dated photo'. Find frequency of the letter 't'

Ex Output:
5

Ex Input:
Sentence: 'the interior of a studio apartment decorated with various pieces of furniture'. Find frequency of the letter 'i'

Ex Output:
7