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: 'a young man riding a skateboard near a forest'. Find frequency of the letter 'd'
2

Sentence: 'a skateboarder is skating in front of bicycles'. Find frequency of the letter 'o'

3