Answer
The tension in each cable is 147 N
Work Step by Step
We can find the angle $\theta$ that each cable makes with the vertical;
$cos(\theta) = \frac{2}{3}$
$\theta = arccos(\frac{2}{3})$
$\theta = 48.2^{\circ}$
The sum of the vertical component of the tension in each cable is equal in magnitude to the weight of the speaker;
$2~T_y = mg$
$2~T~cos(\theta) = mg$
$T = \frac{mg}{2~cos(\theta) }$
$T = \frac{(20~kg)(9.80~m/s^2)}{2~cos(48.2^{\circ})}$
$T = 147~N$
The tension in each cable is 147 N.
