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

Sentence: 'a herd of giraffes in tall african grass'. Find frequency of the letter 'a'
6

Sentence: 'a bird outside standing on a table looking up'. Find frequency of the letter 'b'
2

Sentence: 'many people walk down a busy shade covered sidewalk'. Find frequency of the letter 'd'

4