Solution to Problem 340 | Torsion of thin-walled tube

$T = 2At\tau$
 

Where:
$A = \pi(10^2) + 80(20) = 1914.16 \, \text{mm}^2$

$t = 2 \, \text{mm}$

$T = 600 \, \text{N}\cdot\text{m} = 600\,000 \, \text{N}\cdot\text{mm}$
 

$600\,000 = 2(1914.16)(2)\tau$

$\tau = 78.36 \, \text{ MPa}$           answer