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

[Q]: Sentence: 'the snowboarder wearing a dark helmet sprays snow into the air'. Find frequency of the letter 'w'
[A]: 3

[Q]: Sentence: 'a lady is standing near a luggage stand at the air port'. Find frequency of the letter 'a'
[A]: 9

[Q]: Sentence: 'a red tour bus riding down a street'. Find frequency of the letter 'd'
[A]:
3