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

Sentence: 'a passenger bus that is driving down the street'. Find frequency of the letter 'r'
3

Sentence: 'the man is holding a plastic sled with snow in it next to a child'. Find frequency of the letter 'g'
1

Sentence: 'a man in a swim suit is holding a multicolored umbrella and sitting on the back of a car'. Find frequency of the letter 'g'

2