If R is for fuel efficiency in miles per gallon;
V is for volume of fuel in gallons;
D is for distance in miles,
A useful formula is , or .
Let v be how many gallons used in highway driving.
FUEL EFFICIENCY VOLUME DISTANCE
CITY 28 11-v 28(11-v)
HIGHWAY 33 v 33v
Totals 11 343
-----basic equation to solve.
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and .
City Miles,
Highway Miles,
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You could assign a variable to one of the distances instead, and form an equation that way, using sum of the volumes.