Answer:
The monthly cost for 9 HCF is $38.54
Step-by-step explanation:
<em>The graph is missing; however, the question can still be solved</em>
Given
Slope = 1.55
When monthly cost = $47.84, Amount of water = 15 HCF
Required
Determine the monthly cost for 9 HCF
From the question, we understand that it is a linear function;
Linear functions are of the form

Where y is the function of x and m is the slope
In this case; the function is the monthly water bill
and x is the amount of water
Solving for b
When monthly cost = $47.84, Amount of water = 15 HCF
The function is as follows;


Subtract 23.25 from both sides



Solving for the monthly cost for 9 HCF
Here, we have that



Substitute these values in the linear function; 



<em>Hence, the monthly cost for 9 HCF is $38.54</em>