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

Sentence: 'two persons standing outside a moving sub train'. Find frequency of the letter 'a'
3

Sentence: 'one woman is arranging the other woman's hair'. Find frequency of the letter 'o'
4

Sentence: 'a picture of someone taking a picture of themselves'. Find frequency of the letter 'u'

2