#### Answer

$81b^6$

#### Work Step by Step

When we raise a term inside parentheses to a power, we must raise each part of the term to that power, and then multiply. To raise a power to a power, we simply multiply the exponents. Therefore, $$(9b^3)^2=9^2\cdot (b^3)^2=81\cdot b^{3\times 2}=81b^6$$