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: 'three young people goofing around; one of the guys has a football, the girl has a teddy bear'. Find frequency of the letter 'd'
3

Sentence: 'a hand holding a small red and yellow apple'. Find frequency of the letter 'a'

6