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

Sentence: 'a train going over a bridge with some buildings in the background'. Find frequency of the letter 'd'
3

Sentence: 'two bigger elephants standing with a small elephant'. Find frequency of the letter 't'
5

Sentence: 'a man is holding a baseball bat swinging at the ball'. Find frequency of the letter 'i'

4