How do you represent `"2-methyl, 3-ethylnonane"`?

Structural formula:(Hydrogen is attached to complete Every carbon's valency {but I've not shown here as it is understood, so don't get confused)

`color(white)(a.aaaaaaaaaaa)"CH"_2-"CH"_3`
`color(white)(aaaaaaaaaaaaa)|`
`color(white)(aa.aa)"C"-"C"-"C"-"C"-"C"-"C"-"C"-"C"-"C"`
`color(white)(aaaaaaaaa)|`
`color(white)(aaaaaaaa.)"CH"_3`

Condensed Structural formula:

`"CH"_3-"CH"("CH"_3)-"CH"("CH"_2-"CH"_3)-"CH"_2-"CH"_2-"CH"_2-"CH"_2-"CH"_2-"CH"_3`

Draw the alkane parent, the nonane:

`"H"_3"CCH"_2"CH"_2"CH"_2"CH"_2"CH"_2"CH"_2"CH"_2"CH"_3`

Single out the carbons on the chain that require substitution: `"C"_2` and `"C"_3`:

`"H"_3"C"color(red)("C")"H"_2color(red)("C")"H"_2"CH"_2"CH"_2"CH"_2"CH"_2"CH"_2"CH"_3`

Substitute these positions with `"methyl"` and `"ethyl"` groups:

`"H"_3"C"color(red)("C")"H"("CH"_3)color(red)("C")"H"("CH"_2"CH"_3)"CH"_2"CH"_2"CH"_2"CH"_2"CH"_2"CH"_3`

Of course, you could condense this a bit; it is important to get the condensed formula right, i.e. `"C"_12"H"_26`, i.e. this follows the general formula, `C_nH_("2n+2")`, a saturated alkane as required.