Travel Time via Two Routes

In a certain city, two routes, $A$ and $B$, are used for travel. The time taken in hours can be described by the following system of equations:

$$ 3x + 4y = 24 $$

$$ 6x - 2y = 18 $$

where $x$ is the time taken using route $A$, and $y$ is the time taken using route $B$. If Isabel chooses the route that requires the least time, what is the total time she will take?