Answer :
let's firstly convert the mixed fraction to improper fraction and then proceed from there.
A)
[tex]\stackrel{mixed}{16\frac{2}{3}}\implies \cfrac{16\cdot 3+2}{3}\implies \stackrel{improper}{\cfrac{50}{3}} \\\\[-0.35em] \rule{34em}{0.25pt}\\\\ \begin{array}{ccll} miles&gallons\\ \cline{1-2} 305&\frac{50}{3}\\[1em] x&1 \end{array}\implies \cfrac{305}{x}=\cfrac{~~ \frac{50}{3}~~}{1}\implies \cfrac{305}{x}=\cfrac{50}{3}\implies 915=50x \\\\\\ \cfrac{305}{50}=x\implies \cfrac{183}{10}=x\implies 18\frac{3}{10}=x[/tex]
B)
[tex]\begin{array}{ccll} miles&gallons\\ \cline{1-2} 305&\frac{50}{3}\\[1em] 549&g \end{array}\implies \cfrac{305}{549}=\cfrac{~~ \frac{50}{3}~~}{g}\implies \cfrac{305}{549}=\cfrac{~~ \frac{50}{3}~~}{\frac{g}{1}}\implies \cfrac{305}{549}=\cfrac{50}{3}\cdot \cfrac{1}{g} \\\\\\ \cfrac{305}{549}=\cfrac{50}{3g}\implies 915g=27450\implies g=\cfrac{27450}{915}\implies g = 30[/tex]