Instructions: In this task, you need to replace a letter in the sentence with another given letter.
Input: Sentence: 'a slice of cake with icing on three sides, a knife and fork beside it, on a wooden table surface with a knot area visible in the wood'. Replace the letter 'o' with 'z' in the sentence.
Output:
a slice zf cake with icing zn three sides, a knife and fzrk beside it, zn a wzzden table surface with a knzt area visible in the wzzd