Answer:
The car's average 18 number of miles per gallon
Step-by-step explanation:
The car has different efficiencies depending if its used on highway or city streets.
The efficiency on a highway is:

The efficiency for city driving is:

We now that the car uses twice as many gallons for city driving as for highway driving. This means that, for every gallon consumed, 2/3 are for city driving and 1/3 are for highway driving.
Then, we can calculate how many miles makes the car on average as:

It's a reflection over the y axis because 'a' represents 'x' and if 'a' is negative it flips to the other side leave 'b/y' to remain the same
24 to the power of 4
24x10x10x10x10 = 240,000
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