In a 30-60-90 triangle, the ratios of the lengths of the sides are as follows:
- The side opposite the 30-degree angle (let's call it \( a \)) is \( x \).
- The side opposite the 60-degree angle (let's call it \( b \)) is \( x\sqrt{3} \).
- The hypotenuse (let's call it \( c \)) is \( 2x \).
From your question, we know that the side opposite the 60-degree angle \( b \) is \( 6\sqrt{3} \). According to the properties of a 30-60-90 triangle, we can set up the equation:
\[ b = x\sqrt{3} \]
Setting \( b = 6\sqrt{3} \), we have:
\[ x\sqrt{3} = 6\sqrt{3} \]
To solve for \( x \), divide both sides by \( \sqrt{3} \):
\[ x = 6 \]
Now that \( x \) is known, we can find the length of the hypotenuse \( c \):
\[ c = 2x = 2(6) = 12 \]
Thus, the length of the hypotenuse is \( \boxed{12} \).