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

Sentence: 'a birthday cake with a number one and three candle'. Find frequency of the letter 'w'
1

Sentence: 'the two dogs are playing in the pen together'. Find frequency of the letter 'o'
3

Sentence: 'a group of people standing around a  busy street'. Find frequency of the letter 'n'

3