As an avid biker, you've come to realize that your top speed is really an air speed, not a ground speed, because air resistance is very noticeable when you ride fast. You like to ride at top speed for exactly an hour every day, and you know that on a calm day, you can ride \(20 \mathrm{~km}\) before having to turn around and come back the same way. Today, though, you have a \(20-\mathrm{km} / \mathrm{h}\) head wind for the first leg of the trip (which of course is a tailwind on the way back). You must be back home in an hour, so you look at your map. What top speed can you achieve today?