#### Answer

The answer is $12\sqrt {5}$.

#### Work Step by Step

The given expression is
$8\sqrt {45}+2\sqrt 5-7\sqrt {20}$
Factor the number under root.
=$8\sqrt {5\cdot 3 \cdot 3}+2\sqrt 5-7\sqrt {5\cdot 2\cdot 2}$
Simplify.
=$8\cdot 3\sqrt {5}+2\sqrt 5-7\cdot 2\sqrt {5}$
=$24\sqrt {5}+2\sqrt 5-14\sqrt {5}$
=$26\sqrt {5}-14\sqrt {5}$
=$12\sqrt {5}$.