1. **State the problem:** Find the 4th root of $3^{12}$. 2. **Recall the formula for roots and exponents:** The $n$th root of $a^m$ can be written as $$\sqrt[n]{a^m} = a^{\frac{m}{n}}.$$ This means taking the root is equivalent to raising the base to the power of the fraction $\frac{m}{n}$. 3. **Apply the formula:** Here, $a=3$, $m=12$, and $n=4$, so $$\sqrt[4]{3^{12}} = 3^{\frac{12}{4}}.$$ 4. **Simplify the exponent:** $$3^{\frac{12}{4}} = 3^{\cancel{\frac{12}{4}}} = 3^3$$ 5. **Calculate the power:** $$3^3 = 3 \times 3 \times 3 = 27.$$ 6. **Final answer:** The 4th root of $3^{12}$ is **27**. Therefore, the correct choice is B 27.