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

Sentence: 'a line of people on motorcycles on the road'. Find frequency of the letter 'e'
5

Sentence: 'a yellow fire hydrant in the forefront of a roadway'. Find frequency of the letter 'r'
5

Sentence: 'a large round mirror sitting up on an orange pole'. Find frequency of the letter 'e'

3