Suppose that the number a satisfies the equation 4=a+a^{-1}. What is the value of a^{4}+a^{-4} ?

**Answer Choices**

A. 164

B. 172

C. 192

D. 194

E. 212

Suppose that the number a satisfies the equation 4=a+a^{-1}. What is the value of a^{4}+a^{-4} ?

**Answer Choices**

A. 164

B. 172

C. 192

D. 194

E. 212