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

[Q]: Sentence: 'vanity sitting atop a base with two doors and a mirror overhead'. Find frequency of the letter 'n'
[A]: 3


[Q]: Sentence: 'tow birds flying by a long necked crane'. Find frequency of the letter 'f'
[A]: 1


[Q]: Sentence: 'a flock of seagulls flying over a beach'. Find frequency of the letter 's'
[A]:
2