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

Sentence: 'a herd of zebra standing on top  of a grass covered field'. Find frequency of the letter 'e'
5

Sentence: 'people playing wii bowling in a modern library'. Find frequency of the letter 'o'
3

Sentence: 'two women and a man strike a pose as an airplane sits behind them'. Find frequency of the letter 'd'

2