Ivan does not say anything because he cannot speak.
After Rainsford comes to Zaroff's door, Ivan answers with a gun pointed at Rainsford. Rainsford tries to talk to Ivan, but he does not respond. When Zaroff comes to meet them he explains that even though Ivan is incredibly strong, he is "deaf and dumb" which means he is unable to hear or speak.
The store display rotates 40 times every half hour meaning that it will rotate 80 times every hour. To find how many times it will rotate in 4 hours, you can do 80 times 4. This is 320 rotations.
Also, please try and correctly list your question as this does not pertain to this subject.
Frederick Douglass wrote an autobiographical slave narrative.