Solve the Equation $\log _ { 7 } \sqrt { 7^6 } = x$

Multiple Choice

Solve the equation.
- $\log _ { 7 } \sqrt { 7^6 } = x$

A) $\{ \sqrt { 3 } \}$
B) $\{ 42 \}$
C) $\{ 3 \}$
D) $\{ 21 \}$