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

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

Ex Output:
5

Ex Input:
Sentence: 'a bedroom with a neatly made bed and a laptop'. Find frequency of the letter 'l'

Ex Output:
2

Ex Input:
Sentence: 'an decorated white elephant statue with a bull's eye painted on it'. Find frequency of the letter 'a'

Ex Output:
6