Question $4$

Two moons orbit a planet in nearly circular orbits. Moon $\backslash (\backslash$boldsymbol$\{$A$\}\backslash )$ has orbital radius $\backslash (\backslash$boldsymbol$\{$r$\}\backslash ),$ and moon $\backslash (\backslash$boldsymbol$\{$B$\}\backslash )$ has orbital radius $\backslash (4\backslash$boldsymbol$\{$r$\}\backslash ).$ Moon $\backslash (\backslash$boldsymbol$\{$A$\}\backslash )$ takes $20$ days to complete one orbit. How long does it take moon $\backslash (\backslash$boldsymbol$\{$B$\}\backslash )$ to complete an orbit?$40$ d$320$ d$20$ d$80$ d$160$ d