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

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

Sentence: 'a bird outside standing on a table looking up'. Find frequency of the letter 'b'
2

Sentence: 'there are several telephones and two lap tops on the desk'. Find frequency of the letter 's'
4