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

Sentence: 'a toilet filled with a brown liner and dirty water'. Find frequency of the letter 't'
5

Sentence: 'a little boy standing near a couch and a table'. Find frequency of the letter 'i'
2

Sentence: 'a red and yellow double decker bus driving down a street'. Find frequency of the letter 'n'

3