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

Example Input: Sentence: 'a cat got caught hiding in the cupboard'. Replace the letter 'i' with 'u' in the sentence.
Example Output: a cat got caught hudung un the cupboard

Example Input: Sentence: 'a cat sits on the floor next to a purse'. Replace the letter 'a' with 'b' in the sentence.
Example Output: b cbt sits on the floor next to b purse

Example Input: Sentence: 'this is a birthday cake for someones first birthday'. Replace the letter 'o' with 't' in the sentence.
Example Output:
this is a birthday cake ftr stmetnes first birthday