Answer
$$\frac{a^{5}}{2}$$
Work Step by Step
Raise each factor in the parentheses to the second power:
$$\frac{(3a^{3})^{2}}{18a}=\frac{(3)^{2}(a^{3})^{2}}{18a}.$$
Multiply exponents to raise a power to a power:
$$\frac{9a^{3\times 2}}{18a}=\frac{9a^{6}}{18a}.$$
To divide powers of the same base, subtract the exponents:
$$\frac{a^{6-1}}{2}=\frac{a^{5}}{2}.$$
