How do the words muttered sentences, half-uttered screams that seemed smothered best enhance the tone of this passage

They indicate an otherworldly atmosphere around the narrator.

Explanation:

Mark Twain's "A Ghost Story" is a ghost story about how the narrator experienced during his stay at a hotel. The story seems to be based on the Cardiff Giant, a monster carved out of stone and buried in the ground, only to emerge oftentimes to 'scare' people.

The narrator reveals how he heard "muttered sentences; half-uttered screams that seemed smothered violently;" during his first night at the "old building". This tone, with the discovery of the "[footprint] so vast that in comparison [his] was but an infant's" presents an otherworldly atmosphere, a sense of horror and suspense. By using these words to describe the sounds he heard along the hallway while listening intently, the narrator presents us with a scene that is scary and even intriguing.

we know that, volume of a rectangular prism is given by :

✿   {length × width × height}

given : the length of rectangular prism = 5.5

given : the width of rectangular prism = 6

given : the height of rectangular prism = 3

⇒ the volume of given rectangular prism = {5.5 × 6 × 3}

⇒ the volume of given rectangular prism = 99