Exponential equation are functions defined by 
The equation that could represent Rainey graph must take the form 
<h3>How to determine the equation</h3>
An exponential equation is represented as:

Where:
- a represents the initial value
- b represents the rate
The initial value (a) is 15.
So, the equation becomes

The graph is not given;
So, the equation cannot be determined.
Assume that the rate is 2.
Then the function would be: 
Read more about exponential functions at:
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For this case we have the following system of equations:

Equating the values of y we have:

From here, we can clear the value of x.
We have then:

Then, we look for the value of y.
For this, we substitute x in any of the equations:
Answer:
The ordered pair solution of the system of equations, is given by:
To convert gallons to pints, multiply the gallons by 8. Since there are 4 quarts in a gallon and 2 pints in each quart, you multiply by 8 since 4*2 is 8.