The answer is c. Both a and b which is distance and time.
In order to get or determine the speed, we need to have both time and distance.
The formula would be :
speed = distance / time
And here are another important note to get the time and distance
time = distance / speed
Distance = speed x time
It is always important to remember these 3 formulas to be able to solve given
situations about speed, time and distance.