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

Ex Input:
Sentence: 'four women around a man sitting in front of a cake'. Find frequency of the letter 'o'

Ex Output:
5

Ex Input:
Sentence: 'a red stop sign with street signs above it'. Find frequency of the letter 't'

Ex Output:
5

Ex Input:
Sentence: 'people walk on the sidewalk near the red traffic light'. Find frequency of the letter 'i'

Ex Output:
3