#10 Errata at 21:39

For simple substituents, multiplier prefixes (di-, tri- tetra- etc.) are ignored as told by Shashi sir earlier. Therefore, the right name for the compound is:

3-ethyl-2,3-dimethyl hex-4-en oic acid 

and not 

2,3-dimethyl-3-ethyl hex-4-en oic acid

as written by sir next. 

Reference Doubt Link