Use the Distributive Property to Help Simplify the Following Expression $- 3 \sqrt { 4 x } + 3 \sqrt { 9 x } + 5 \sqrt { 16 x }$

Use the distributive property to help simplify the following expression. All variables represent positive real numbers. $- 3 \sqrt { 4 x } + 3 \sqrt { 9 x } + 5 \sqrt { 16 x }$