Answer: second option.
Step-by-step explanation:
By definition, the measure of any interior angle of an equilateral triangle is 60 degrees.
Based in this, we know that the measusre of the angle ∠SRT is:
[tex]\angle SRT=\frac{60\°}{2}=30\°[/tex]
The, we can find the value of "y":
[tex]y+12=30\\y=30-12\\y=18[/tex]
To find the value of "x", we must use this identity:
[tex]cos\alpha=\frac{adjacent}{hypotenuse}[/tex]
In this case:
[tex]\alpha=30\°\\adjacent=x\\hypotenuse=RU=RS=4[/tex]
Substituting values and solving for "x", we get:
[tex]cos(30\°)=\frac{x}{4}\\\\4*cos(30\°)=x\\\\x=\sqrt{12}[/tex]
