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

Sentence: 'two men are playing a video game as another sits watching'. Find frequency of the letter 'a'
7

Sentence: 'a mixed bouquet of flowers in a glass vase set before a window'. Find frequency of the letter 'w'
3

Sentence: 'a young man walking along a river bank near a woman riding a surfboard'. Find frequency of the letter 'n'

8