(C₂H₅)₃C - CH₂- CH₂ - C(C₂H₅)₃
Also, it can be written as CH₃-CH₂-(C₂H₅)₂C - CH₂- CH₂ - C(C₂H₅)₂-CH₂-CH₃
So, there are four ethyl groups, two at 3rd carbon and two at 6th carbon , these are substituents so prefix '3,3,6,6-tetra ethyl' is added with the root word 'oct' (C - 8) and we have suffix 'ane'
Prefix + root word + suffix
3,3,6,6- tetraethyl octane