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

Example Input: Sentence: 'woman pushing a cart of luggage in a transportation terminal'. Replace the letter 'a' with 'w' in the sentence.
Example Output: womwn pushing w cwrt of luggwge in w trwnsportwtion terminwl

Example Input: Sentence: 'a group of giraffe standing on top of a dirt field'. Replace the letter 'a' with 'y' in the sentence.
Example Output: y group of giryffe stynding on top of y dirt field

Example Input: Sentence: 'a woman is sitting at a bar smiling for a picture'. Replace the letter 'i' with 'n' in the sentence.
Example Output:
a woman ns snttnng at a bar smnlnng for a pncture