Simplify Assume That All Variables Represent Positive Real Numbers $\sqrt{9 x}+\sqrt{36 x}-\sqrt{49 x}$

Short Answer

Simplify. Assume that all variables represent positive real numbers.
(a) $\sqrt{9 x}+\sqrt{36 x}-\sqrt{49 x}$
(b) $(2-\sqrt[3]{2})(2+\sqrt[3]{4})$
(c) $(\sqrt{x y}-1)(\sqrt{x y}+1)$