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

Sentence: 'a man with a skateboard that is in the street'. Find frequency of the letter 'o'
1

Sentence: 'a double decker bus with a lot of people on board'. Find frequency of the letter 'l'
3

Sentence: 'cows standing together outside of a thatched roof building'. Find frequency of the letter 'u'

2