- The elasticity of demand is \( E(x) = 1 \).
- The elasticity at \( x = 7 \) is \( E(7) = 1 \), indicating unit elasticity.
- There are no specific values of \( x \) for which total revenue is maximized.
Thus, the final answers are:
\[
\boxed{E(x) = 1}
\]
\[
\boxed{E(7) = 1 \text{ (unit elasticity)}}
\]
\[
\boxed{\text{No specific } x \text{ for maximum total revenue.}}
\]