(1) The train travels 4 miles per gallon.
(2) The slope of the graph is 
Explanation:
(1) The miles that train travels per gallon is given by

Dividing, we have,

Thus, the train travels 4 miles per gallon.
(2) To determine the slope, let us consider two points from the graph.
The coordinates are
and 
Thus, substituting the coordinates in the slope formula, we get,

Simplifying, we have,

Thus, the slope of the graph is 
By "slope" I assume you mean slope of the tangent line to the parabola.
For any given value of <em>x</em>, the slope of the tangent to the parabola is equal to the derivative of <em>y</em> :

The slope at <em>x</em> = 1 is 5:

The slope at <em>x</em> = -1 is -11:

We can already solve for <em>a</em> and <em>b</em> :


Finally, the parabola passes through the point (2, 18); that is, the quadratic takes on a value of 18 when <em>x</em> = 2:

So the parabola has equation

Both are right b/c like sean says you can add zero and itll still be -100 but candice is also right b/c because you can add any # to that -100 but you can also add a negative # to get it back to -100. for example: -100+23= -77 but if you also add a negative 23 it would be right back to -100.
Step 1: Add together the known angles.
Step 2: Subtract the sum from 180°.