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

Sentence: 'a child sitting a table with a pizza in front of him'. Find frequency of the letter 'h'
3

Sentence: 'a group of workers washing and cleaning fruits and vegetables'. Find frequency of the letter 'i'
3

Sentence: 'several zebra are standing in a field with trees in the background'. Find frequency of the letter 's'

3