Answer: 36.4 miles per gallon!
Step-by-step explanation: To get your answer....divide the y (miles driven) by x (gallons used). Each divided gives you the answer of 36.4 which is the constant of proportionality between the number of miles driven and the number of gallons used.
For example: 691.6 divided by 19= 36.4
1528.8 divided by 42=36.4
1638 divided by 45=36.4