If an object moves along a straight line, the distance travelled can be represented by a distance-time graph. In a distance-time graph, the gradient of the line is equal to the speed of the object. The greater the gradient (and the steeper the line) the faster the object is moving.
Speed = distance ÷ time
Distance = speed × time
Time = distance ÷ speed
To calculate one of the variables (speed, distance or time) we need the other two.