Question

A plane is 500 miles west of city A, and is flying west at 400 miles per hour. How long will it take for the plane to be 1920 miles away from city A?

Answer 1

so, the plane is already 500 miles west of A, so, to be 1920 miles away from A, it simply needs to keep on going for 1920 - 500, or 1420 more miles

now, the plane is going at 400miles in one hour, how long will it take it to cover 1420 miles?

well
`\bf \begin{array}{ccllll} miles&hours\\ \textendash\textendash\textendash\textendash\textendash\textendash&\textendash\textendash\textendash\textendash\textendash\textendash\\ 400&1\\ 1420&x \end{array}\implies \cfrac{400}{1420}=\cfrac{1}{x}`

solve for "x"