Part A: Line 6
Alliteration is the repetition of the same sound at the beginning of a group of words. Line 6 is "Late spring sky, Ms. Marcus says, Almost summer sky." The /s/ sound is repeated fives times at the beginning of the words in this line of poetry.
Part B: It sounds soothing and peaceful.
The /s/ sound is a soothing and peaceful sound. Even the words soothing and peaceful have the /s/ sound. It creates a soothing a peaceful mood just like the long days at the end of spring and beginning of summer.