Answer
$f_s=51.4N$
Work Step by Step
Let's choose the axis of rotation to be at the point where 2 sides meet each other and examine only 1 board out of the two. The length of the board is denoted $L$.
There are 3 forces that produce torques affecting the rotation of the board.
Because the board is in equilibrium, $$\sum\tau=0.25WL+0.866f_sL-0.5NL=0$$ $$0.25W+0.866f_s-0.5N=0$$
$W$ and $N$ are also 2 vertical forces of the system. The net vertical force is zero, so they balance each other, which means $W=N=178N$
$$-0.25W+0.866f_s=0$$ $$f_s=\frac{0.25W}{0.866}=51.4N$$
