Final answer:
You turn your front wheels all the way to the left when parking downhill with a curb to ensure that if the vehicle's brakes fail, it will roll into the curb, not into the street.
Step-by-step explanation:
When parking on a hill with a curb, you generally adjust the position of your front wheels to prevent your vehicle from rolling into traffic if the brakes fail. For uphill parking where a curb is present, you would turn your wheels away from the curb, so the rear of the vehicle would roll into the curb if the brakes were to give out. Conversely, when parking downhill, you turn your wheels all the way to the left, which means towards the curb (in countries where you drive on the right side of the road), again so the vehicle will roll into the curb and not into the street. If there is no curb, you would turn your wheels all the way to the right, whether you are parking uphill or downhill, so the vehicle will roll off the road rather than into traffic.