What is the correct IUPAC name for 3-methyl 6-3 hexene?

I think you need to work on the nomenclature protocols…

$\text{n-hexane}$ is $H_{3}\stackrel{1}C-CH_{2}CH_{2}CH_{2}CH_{2}\stackrel{6}CH_{3}$ …

$\text{1-hexene}$ is $H_{2}\stackrel{1}C=CHCH_{2}CH_{2}CH_{2}CH_{3}$ …

$\text{3-hexene}$ is $H_{3}C-CH_{2}\stackrel{3}CH=CHCH_{2}CH_{3}$ …and it has TWO isomeric forms…which are…? And clearly there are other structural, and geometric isomers…

Over to you….