In this case they ask us to calculate the time in hours that are in those distances, for this we have the speed and the distance, we know that speed is equal to:
v = d / t
therefore the time would be:
t = d / t
we must pass the distance that is in kilometers to miles, like this:
We know that is a parabola, concave up, with vertex in the origin
So, we may use three horizontal lines for our purpose: any horizontal line above the x axis will intersect the parabola twice. The x axis itself intersects the parabola once on the vertex, while any horizontal line below the x axis won't intercept the parabola.
Here's the examples:
The horizontal line intercepts the parabola twice: the system is solved by
The horizontal line intercepts the parabola only once: the system is which yields which is a repeated solution
The horizontal line intercepts the parabola only once: the system is which yields which is impossible, because a squared number can't be negative.