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

[Q]: Sentence: 'a white toilet sitting next to a bathroom sink'. Find frequency of the letter 'b'
[A]: 1


[Q]: Sentence: 'a ready to eat pizza on a rack'. Find frequency of the letter 'r'
[A]: 2


[Q]: Sentence: 'a glass bowl of raw broccoli, a ceramic bowl of raw green chili peppers, and steel bowl of raw daikon'. Find frequency of the letter 'a'
[A]:
9