Add or Subtract $\sqrt { 112 } + \sqrt { 448 }$

Multiple Choice

Add or subtract. Assume all variables represent positive real numbers.
- $\sqrt { 112 } + \sqrt { 448 }$

A) $- 4 \sqrt { 7 }$
B) $12 \sqrt { 14 }$
C) 84
D) $12 \sqrt { 7 }$