Mensuration (Pyramid, Cones and Spheres) - Volume and Surface Area of Composite Solids

A rubber cable protector is made from a semicircular prism of diameter \(20\) cm and length \(18\) cm.
An isosceles triangular groove runs along its entire length, opening at both ends and along the underside. The triangle has base \(6\) cm, perpendicular height \(4\) cm and two equal sides of \(5\) cm. The shaded region shows the rubber remaining.

Uniform length perpendicular to this view: \(18\) cm

1. Find the area of the rubber cross-section, giving your answer exactly in terms of \(\pi\).

   [2]

2. Calculate the volume of rubber in the protector.

   [1]

3. Before installation, every exposed surface is given a protective coating, including the surfaces inside the groove, both ends and the flat portions of the underside. Calculate the total area coated.

   [3]

Give your answers to (b) and (c) correct to \(1\) decimal place.