## Intermediate Algebra (6th Edition)

$81$
Using $i^2=-1$ and the laws of exponents, the expression $(3i)^4$ simplifies to \begin{array}{l} 3^4i^4 \\= 81(i^2)^2 \\= 81(-1)^2 \\= 81(1) \\= 81 .\end{array}