#### Answer

36.4

#### Work Step by Step

Let $D(20,20)$ be $(x_1,y_1)$. Let $E(30,-15)$ be $(x_2,y_2)$.
Use the distance formula:
$d=\sqrt{(x_2-x_1)^2+(y_2-y_1)^2}$
$d=\sqrt{(30-20)^2+(-15-20)^2}$
$d=\sqrt{10^2+(-35)^2}$
$d=\sqrt{100+1225}$
$d=\sqrt{1325}$
$d=36.4$