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

Sentence: 'many white birds flying above a river that flows in front of a forest'. Find frequency of the letter 'a'
5

Sentence: 'a car accident has slowed traffic as a clean up crew works'. Find frequency of the letter 'f'
2

Sentence: 'a street sign has been knocked on to the ground'. Find frequency of the letter 'g'
2