Explanation:
Right away i notice the 45° angle and the 90° angle in triangle RTQ, this means that the remaining angle must be 180-(90+45)=45°.
If it isn't obvious yet, triangle RTQ is a right isosceles triangle where RT=RQ=x.
Now looking at my other triangle RST
I know that RT=x, RS=2√3 and ST is unknown.
So i cannot apply my Pythagorean theorm.
HOWEVER i do notice 60 degree angle and the 90 degree angle, which means that the last angle must be 180-(90+60)=30° and this triangle (RST) must be a half equilateral triangle;,
Now i can use the relation which describes the relation between the hypotenuse(x) and the side opposite or facing the 60° angle (RS=2√3).
RS=x√3/2
2RS=x√3
2×2√3=x√3
4√3=x√3
4√3/√3=x
x=4 :P