Find the ${10}^{\mathrm{th}}$ term of the geometric sequence in which $a_1=5$ and $r=2$.

Write a recursive formula for the geometric sequence $\{18,6,2,\frac{2}{3},\dots \}$.

Write a formula for the general or $n^{\mathrm{th}}$ term of the geometric sequence where $a_7=1458$ and $r=-3$.