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

[EX Q]: Sentence: 'man riding a skate board down the little board way'. Find frequency of the letter 'k'
[EX A]: 1

[EX Q]: Sentence: 'a man standing on a tennis court holding a racquet'. Find frequency of the letter 's'
[EX A]: 2

[EX Q]: Sentence: 'luggage at an airport on a turn table waiting for pickup'. Find frequency of the letter 'r'
[EX A]:
4