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

[EX Q]: Sentence: 'a couple of items that are on the wall'. Find frequency of the letter 'm'
[EX A]: 1

[EX Q]: Sentence: 'a small boy in a high chair eating a cupcake'. Find frequency of the letter 'i'
[EX A]: 4

[EX Q]: Sentence: 'an extra long bus is driving through the city'. Find frequency of the letter 'b'
[EX A]:
1