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

[Q]: Sentence: 'an image of a street sign with a corner restaurant'. Find frequency of the letter 'u'
[A]: 1


[Q]: Sentence: 'a view from a bathroom shows an open door'. Find frequency of the letter 'o'
[A]: 7


[Q]: Sentence: 'two people under an umbrella while walking down a sidewalk'. Find frequency of the letter 'i'
[A]:
3