If three is five ,and 5 is 4,and 4is4 ,
What is 8

You are counting the number of letters in the spelled number.

3 - three - has 5 letters - Hence, "three is five"

5 - five - has 4 letters - Hence, "five is four"

4 - five - has 4 letters - Hence, "four is four"

8 - eight - has 5 letters - Hence, "eight is five"

look a the sides they are perpendicular

go and ask your mom to you