Answer
15
Work Step by Step
$\sqrt {225}$$\longrightarrow$ factor out perfect squares
$=\sqrt {25\times9}$ $\longrightarrow$use the multiplication property of squre roots
$=\sqrt {25}\times\sqrt 9$$\longrightarrow$simplify
$=5\times3$$\longrightarrow$multiply
$=15$
