A power cable hangs between two poles of equal height, 30 m apart…

A power cable hangs between two poles of equal height, $30$ m apart. A surveyor takes the origin on the ground directly below the lowest point of the cable. The cable then follows the curve $y = 20\cosh\dfrac{x}{20}$ for $-15 \le x \le 15$, with $x$ and $y$ in metres. A cable that hangs under its own weight takes this shape, called a catenary. The cable has a mass of $1.4$ kg for each metre of its length. The supplier wants the length of the cable between the poles, to order the right amount. The line engineer wants the sag, which is how far the lowest point hangs below the top of a pole. The loader wants the mass of the cable. Find the length, the sag and the mass. Give the answers to two decimal places. A straight line between the tops of the poles would be $30$ m, so the cable must be longer than that.