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

Ex Input:
Sentence: 'group of cars on the road with the sun setting behind it'. Find frequency of the letter 'd'

Ex Output:
2

Ex Input:
Sentence: 'a white bowl filled with peeled orange slices'. Find frequency of the letter 's'

Ex Output:
2

Ex Input:
Sentence: 'a truck parked on the dock as a boat approaches'. Find frequency of the letter 's'

Ex Output:
2