Answer: The numbers are 1 and 2
Step-by-step explanation:
(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 
Let x represent the number of the doll.
1.5x=5
x≈3. As a result, they could buy 3 dolls with 5 dollars. Hope it help!