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With a full tank of gas, you can drive 485 miles and your car can go 19 miles per gallon.
Write an equation to model this situation (use m for miles you can drive and g for gallons in the tank).
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This problem requests you to translate English words from the post to Math.
My translation is this
m = 19*g, under the condition 0 <= m <= 485.
The problem does not request you to do something above of it.
So, what @Theo does in his post after establishing an equation, is irrelevant to the problem.
All that they want from you is to create an equation and write the constraint.