Complete the statement. $5\sqrt{98}+10y\sqrt{162}=5\sqrt{2}(?)$

A) $7+9y$
B) $14+81y$
C) $7+18y$
D) $9+14y$
E) $9+7y$

First, simplify the square roots:
$5\sqrt{98} = 5\sqrt{2\cdot49} = 5\cdot7\sqrt{2} = 35\sqrt{2}$
$10y\sqrt{162} = 10y\sqrt{2\cdot81} = 10y\cdot9\sqrt{2} = 90y\sqrt{2}$
Now substitute back into the original equation:
$35\sqrt{2} + 90y\sqrt{2} = 5\sqrt{2}(7 + 18y)$
Therefore, the answer is (C) $7 + 18y$.