Visual warning devices must be visible for how far in both directions when you have broken down?

Answer: B — 150 metres

Visual warning devices, such as hazard lights or road flares, must be visible for at least 150 meters in both directions when a vehicle breaks down on the road. This is to ensure that other drivers have enough time to safely slow down and maneuver around the stranded vehicle. Option A, 100 meters, may not provide adequate notice for drivers to take caution. Option C, 200 meters, and option D, 250 meters, exceed the minimum visibility requirement, but may cause confusion for other drivers as to when to slow down. Therefore, option B, 150 meters, is the most appropriate answer.