Simplify and Write the Answer in Exponential Notation Using Positive $6 ^ { 7 } \cdot 6 ^ { - 4 }$

Simplify and write the answer in exponential notation using positive exponents. $6 ^ { 7 } \cdot 6 ^ { - 4 }$

A) $6 ^ { 3 }$

B) $36 ^ { 3 }$

C) $36 ^ { - 28 }$

D) $6 ^ { - 28 }$