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

Sentence: 'a stop sign near a rail road crossing sign'. Find frequency of the letter 'g'
3

Sentence: 'a lady is standing near a luggage stand at the air port'. Find frequency of the letter 'a'
9

Sentence: 'a man riding a brown horse down a race track'. Find frequency of the letter 'm'

1