Write an Equivalent Expression in Exponential Form $$\log _ { x } 16 = 2$$

Write an equivalent expression in exponential form.
- $$\log _ { x } 16 = 2$$

A) $\{ 18 \}$
B) $\{ 4 \}$
C) $\{ 32 \}$
D) $\{ 8 \}$