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

Sentence: 'a woman sitting in front of a giant slice of cheese pizza'. Find frequency of the letter 'e'
4

Sentence: 'a parking meter painted green with a sign that describes it as not a parking meter'. Find frequency of the letter 's'
4

Sentence: 'a military fighter jet in flight armed with missiles'. Find frequency of the letter 'f'
2