(a) IUPAC name: 3,3-Diethyl pentane
Condensed formula: `C(C_(2)H_(5))_(4)` or `Cet_(4)`
(b) IUPAC name: 4,4-Dipropyl heptane
Condensed formula: `C(C_(3)H_(7))_(4)` or `CPr_(4)`
(c) IUPAC name: 3-Ethyl-4-methyl hexane
Condensed formula: `(C_(2)H_(5))_(2)CHCH(CH_(3))C_(2)H_(5)`
or
`Et_(2)CHCH(Me)Et`