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

Sentence: 'cars parked outside if a retail store'. Find frequency of the letter 'd'
2

Sentence: 'two baseball players high five each other during a game'. Find frequency of the letter 'y'
1

Sentence: 'a long train traveling past tall buildings on train tracks'. Find frequency of the letter 's'

3