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

Ex Input:
Sentence: 'a blue train on a track next to another track'. Find frequency of the letter 'c'

Ex Output:
2

Ex Input:
Sentence: 'one man grabbing another at a table while laughing'. Find frequency of the letter 'n'

Ex Output:
5

Ex Input:
Sentence: 'a fence with a blue umbrella hanging over the side of it'. Find frequency of the letter 'l'

Ex Output:
3