Which two of the following are "like surds"?
$4\sqrt{x}$4√x
$6\sqrt[3]{x^2}$63√x2
$\sqrt{5x}$√5x
$9\sqrt{x^2}$9√x2
$8\sqrt[3]{x}$83√x
$2\sqrt{x}$2√x
Simplify the expression $7\sqrt{u}+3\sqrt{u}$7√u+3√u.
Simplify the expression $11\sqrt{u}-7\sqrt{u}$11√u−7√u.
Simplify the expression $8\sqrt{u}-10\sqrt{u}$8√u−10√u.