Suppose that the weight (in pounds) of an airplane is a linear function of the total amount of fuel (in gallons) in its tank. When graphed, the function gives a line with a slope of 6.2.

Question

Suppose that the weight (in pounds) of an airplane is a linear function of the total amount of fuel (in gallons) in its tank. When graphed, the function gives a line with a slope of 6.2. 
With 52 gallons of fuel in its tank, the airplane has a weight of 2222.4 pounds. What is the weight of the plane with 26 gallons of fuel in its tank?

Steve · Answer

y = 6.2x + b
2222.4 = 6.2*52 + b, so b = 1900

So, we now know that

y = 6.2x + 1900

Just plug in x=26

Or, without even finding b, we know that each gallon of fuel weighs 6.2 pounds, so just subtract 26*6.2 from 2222.4