(c) The thinking distance is the distance travelled during the driver's reaction time. A car was travelling at 13 m/s
The driver's reaction time was 0.6 s
Calculate the thinking distance
Use the equation:
distance travelled = speed x time
Thinking distance =

  distance on the y-axis and time on the x-axis.

explanation:

the instantaneous velocity = change in position/time taken

the slope of the graph should give instantaneous velocity.

  slope of a graph = change in value of y -axis / change in values of x -axis

  comparing both the equations

    change in value of y -axis = change in position

  change in values of x -axis = time taken

so position values should be on the y axis and time values should be on the x axis.

distance on the y-axis and time on the x-axis.

conservation of mass

mass before something happens = mass afterwards