Answer
$5\sqrt 5$
Work Step by Step
Step 1: $\sqrt (45)+\sqrt (20)$
Step 2: $\sqrt (9\times5)+\sqrt (4\times5)$
Step 3: $(\sqrt 9\times\sqrt 5)+(\sqrt 4\times\sqrt 5)$
Step 4: $(3\times\sqrt 5)+(2\times\sqrt 5)$
Step 5: $3\sqrt 5+2\sqrt 5$
Step 6: $5\sqrt 5$
