Question

A car averages 18 miles per gallon of gas in city driving and 27 miles per gallon of gas in highway driving. What is the total number of gallons of gas needed to drive 6x miles in the city and 18x miles on the highway?

Answer 1

6x miles, I gather it means, six times the 18 miles, or 6 * 18 miles
and 18x I gather it means, 18 * 27 miles for the highway

thus
$\bf \begin{array}{ccllll} City\\ miles&gallons\\ \textendash\textendash\textendash\textendash\textendash\textendash&\textendash\textendash\textendash\textendash\textendash\textendash\\ 18&1\\ 6\cdot 18&x \end{array}\implies \cfrac{18}{6\cdot 18}=\cfrac{1}{x}\impliedby \textit{solve for "x"} \\ ----------------------------$
$\bf \begin{array}{ccllll} Highway\\ miles&gallons\\ \textendash\textendash\textendash\textendash\textendash\textendash&\textendash\textendash\textendash\textendash\textendash\textendash\\ 27&1\\ 8\cdot 27&x \end{array}\implies \cfrac{27}{8\cdot 27}=\cfrac{1}{x}\impliedby \textit{solve for "x"}$