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Answer: 
Step-by-step explanation:
Given : The fuel efficiency of car = 7.6 km per kilogram
We also given that
1 mile = 1.609 km
Then, 
1 gallon = 3.785 liters

1 liter of gasoline = 0.729 kg
Then, 

Now, the fuel efficiency of car will be :

Hence, the car’s fuel efficiency in miles per gallon= 4.5
The prove to show that the area of the shaded portion is 18x - 30 is as follows: 3x² + 13x - 30 - 3x² + 5x = 18x - 30
<h3>How to find the area of the shaded region?</h3>
The area of the shaded region can be represented as follows:
area of the shaded region = area of rectangle - area of triangle
Therefore,
area of the rectangle = (x + 6)(3x - 5)
area of the rectangle = 3x² - 5x + 18x - 30
area of the rectangle = 3x² + 13x - 30
area of triangle = 1 / 2 × 2x × 3x - 5
area of triangle = 3x² - 5x
Therefore,
area of the shaded portion = 3x² + 13x - 30 - 3x² + 5x
area of the shaded portion = 18x - 30
learn more on area here: brainly.com/question/21208569
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