Which classification describes $\sqrt{-9}$?

Compute $(3-2i)+(-5+7i)+(1+4i)$ and simplify to standard form.

Simplify $\sqrt{-72}$ fully, extracting perfect-square factors and following notation conventions.

What is the value of $i^{13}$?

Compute $\frac{1+2i}{3-4i}$ in standard form $a+bi$, reduced to lowest terms.

Find a real $x$ such that $(x+2i)(1+3i)=7+11i$.