Express the Following as a Single Fraction Involving Positive Exponents $$4 x ^ { - 3 } - 5 x ^ { - 7 }$$

Multiple Choice

Express the following as a single fraction involving positive exponents only. $$4 x ^ { - 3 } - 5 x ^ { - 7 }$$

A) $- \frac { 1 } { x ^ { 10 } }$
B) $4 x ^ { 7 } - 5 x ^ { 3 }$
C) $\frac { 4 x ^ { 4 } - 5 } { x ^ { 7 } }$
D) $\frac { 4 x ^ { 4 } - 5 } { x ^ { 6 } }$
E) $\frac { 1 } { 4 x ^ { 7 } - 5 x ^ { 3 } }$