#### Answer

$s$$\sqrt 3$

#### Work Step by Step

We know that any triangle in this figure has a hypotenuse of $s$ and a height of $\frac{s}{2}$. We know that this is the height because it is given that the vertical blue crosspiece is $s$, and half of $s$ is $\frac{s}{2}$. This triangle embodies the properties of a 30-60-90 triangle, so using the properties of this triangle, we can solve for the missing side length. After finding the missing side length, make sure to multiply it by 2 to find the length of the horizontal red crosspiece: