Draw the structures for 4-ethyl-2,2-dimethylheptane and 3-ethyl-2,4-dimethylhexane.

$$
\text{CH}_3-\text{C}(\text{CH}_3)_2-\text{CH}_2-\text{CH}(\text{CH}_2\text{CH}_3)-\text{CH}_2-\text{CH}_2-\text{CH}_3
$$
Or in skeletal form:
$$
\boxed{
\begin{tikzpicture}[scale=0.7]
\draw (0,0) -- (1,0) -- (2,1) -- (3,0) -- (4,1) -- (5,0) -- (6,0);
\draw (1,0) -- (1,-1);
\draw (1,0) -- (0.5,0.8);
\draw (3,0) -- (3,-1);
\end{tikzpicture}
}
$$
(Note: The skeletal structure above represents the main chain with branches. The first carbon is implicitly $\text{CH}_3$, the second carbon has two $\text{CH}_3$ groups, the third is $\text{CH}_2$, the fourth has a $\text{CH}_2\text{CH}_3$ group, and the remaining are $\text{CH}_2$ and $\text{CH}_3$.)

$$
\text{CH}_3-\text{CH}(\text{CH}_3)-\text{CH}(\text{CH}_2\text{CH}_3)-\text{CH}(\text{CH}_3)-\text{CH}_2-\text{CH}_3
$$
Or in skeletal form:
$$
\boxed{
\begin{tikzpicture}[scale=0.7]
\draw (0,0) -- (1,0) -- (2,1) -- (3,0) -- (4,1) -- (5,0);
\draw (1,0) -- (1,-1);
\draw (2,1) -- (2,2);
\draw (3,0) -- (3,-1);
\end{tikzpicture}
}
$$
(Note: The skeletal structure above represents the main chain with branches. The first carbon is implicitly $\text{CH}_3$, the second carbon has a $\text{CH}_3$ group, the third has a $\text{CH}_2\text{CH}_3$ group, the fourth has a $\text{CH}_3$ group, and the remaining are $\text{CH}_2$ and $\text{CH}_3$.)