Triangle RST is a special triangle; it's a 30-60-90 triangle. Since side RS is 2root3, we know that side RT has to be 4.
Triangle RTQ is also a special triable, it's a 45-45-90 triangle. We know that sides RT and RQ have to be congruent.
We know already that side RT is 4, so side RQ has to be 4 as well.
X=4