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

Sentence: 'a man hitting a tennis ball with a tennis racquet'. Find frequency of the letter 't'
6

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

Sentence: 'a clock on a castle with a few clouds in the sky'. Find frequency of the letter 't'

3