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

Sentence: 'there is a person standing on a blue towel'. Find frequency of the letter 'n'
4

Sentence: 'a red fire hydrant opened and spilling water'. Find frequency of the letter 'd'
4

Sentence: 'a royal blue jar in a travel terminal'. Find frequency of the letter 'v'

1