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

[Q]: Sentence: 'a large motorcycle that has a man dressed in old clothing next to it'. Find frequency of the letter 'a'
[A]: 6

[Q]: Sentence: 'an commercial airline airplane flies above the clouds'. Find frequency of the letter 'n'
[A]: 3

[Q]: Sentence: 'the last octave of piano keys on a keyboard with a sound board'. Find frequency of the letter 'd'
[A]:
3