What is the length of SQ

I believe you use power of a point for this problem.

https://artofproblemsolving.com/wiki/index.php/Power_of_a_Point_Theorem

Here's a nice article to read if you don't know it.

6^2 = x*(x+5)

36 = x^2 + 5x

x = 4

I hope that's correct :))

=^._.^=

ah nvm, read that wrong