During an experiment, the level of water in a cylindrical tank remained constant at 7 m for 6 hours.
a. (i) Taking the horizontal axis to represent time (in hours) and the vertical axis to represent water level (in metres), write the linear equation that models this situation.
b. (ii) Draw the graph of the equation for time from 0 h to 6 h.
c. (iii) From your graph, read the water level at t=3.5 h and at t=6 h, and state your observation.
d. (iv) If the water level were instead constant at 0 m, what would be the corresponding linear equation? Describe how its graph would appear in relation to the axes.