$3$
1. If the positive number $n$ is a root of the equation $x^{2}+3 x-28=0$, then
$$
\frac{1}{\sqrt{n}+\sqrt{n+2}}+\frac{1}{\sqrt{n+2}+\sqrt{n+4}}+\cdots+\frac{1}{\sqrt{n+58}+\sqrt{n+60}}=
$$
$\qquad$