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

Sentence: 'pizza with different vegetables sitting on top of a wooden slab'. Find frequency of the letter 'o'
5

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

Sentence: 'a blue rail car, followed by a green rail car, driving in a residential neighborhood'. Find frequency of the letter 'e'

7