The fuel efficiency (in miles per gallon) of an SUV depends on its weight according to the formula†
E = 0.000 001 6x2 − 0.016x + 54 (1,800 ≤ x ≤ 5,400)

where x is the weight of an SUV in pounds. According to the model, what is the weight of the least fuel-efficient SUV?
x = lbs

Would you trust the model for weights greater than the answer you obtained? Explain.
The model (is) or (is not) trustworthy for vehicle weights larger than____ pounds because it predicts fuel economy with increasing weight. Also, ____ is close to of the function.