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

[Q]: Sentence: 'a red fire hydrant opened and spilling water'. Find frequency of the letter 'd'
[A]: 4


[Q]: Sentence: 'two people holding their skies in a snowy resort'. Find frequency of the letter 'n'
[A]: 3


[Q]: Sentence: 'a car with doors open sitting in front of  a group of motorcycles'. Find frequency of the letter 'i'
[A]:
4