Answer:
 y axis denotes the level of water in cylinder
x axis denotes the time 
Step-by-step explanation:
Given : At 1 p.m. cylinder is 80% full i.e. 0.80.
            At 2 p.m. cylinder is 65% full i.e. 0.65.
Solution :
time(x) :        1                    2
level (y) :      0.80            0.65
Using these points we can plot the graph (refer the attached figure)
In the figure y axis denotes the level of water in cylinder
x axis denotes the time 
We can also find the equation of the graph by using two point slope form :
  ---a
Where m is the slope 

Since  
            
Thus  slope (m) =


Now putting values in equation a



Thus the required equation of the situation or the graph is 

THE GRAPH IS ATTACHED AND Y INTERCEPT DENOTES THE LEVEL OF WATER