In this task, you need to replace a letter in the sentence with another given letter.

Example Input: Sentence: 'a safari setting at a zoo with two giraffes and a zebra'. Replace the letter 'n' with 'g' in the sentence.
Example Output: a safari settigg at a zoo with two giraffes agd a zebra

Example Input: Sentence: 'a couple of giraffe standing next to each other'. Replace the letter 't' with 'c' in the sentence.
Example Output: a couple of giraffe scanding nexc co each ocher

Example Input: Sentence: 'a cake sitting on top of a computer keyboard'. Replace the letter 'o' with 'f' in the sentence.
Example Output:
a cake sitting fn tfp ff a cfmputer keybfard