Answer
$2 \pi (4 -\pi) $
Work Step by Step
We need to integrate the integral as shown below:
$ Volume = \int_0^{\pi/4} (2 \pi) (4) \times (tan^2 x) dx \\ =8 \pi \int_0^{\pi/4} (\sec^2 x-1) dx \\=8 \pi [\tan x-x] _0^{\pi/4} \\= 2 \pi (4 -\pi) $