Instructions: In this task, you need to replace a letter in the sentence with another given letter.
Input: Sentence: 'a delivery van and a passenger buss drive down a street in a city'. Replace the letter 'y' with 'k' in the sentence.
Output:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
a deliverk van and a passenger buss drive down a street in a citk