Add or Subtract $$5 \sqrt [ 3 ] { a } + \sqrt [ 3 ] { 64 a }$$

Multiple Choice

Add or subtract. Assume all variables represent positive real numbers.
- $$5 \sqrt [ 3 ] { a } + \sqrt [ 3 ] { 64 a }$$

A) $20 \sqrt [ 3 ] { a }$
B) $9 \sqrt [ 3 ] { a }$
C) $5 \sqrt [ 3 ] { a } + \sqrt [ 3 ] { 64 a }$
D) $6 \sqrt [ 3 ] { 64 a }$