Application problem with a linear function: Finding a coordinate given two points

Question

Suppose that the weight (in pounds) of an airplane is a linear function of the amount of fuel (in gallons) in its tank. When carrying 20 gallons of fuel, the airplane weighs 2224 pounds. When carrying 55 gallons of fuel, it weighs 2441 pounds. How much does the airplane weigh if it is carrying 70 gallons of fuel?

Answer 1

The wight is a linear function. We see that 35 gallons (55 - 20) of fuel weigh 217 pounds (2441 - 2224). That's 217/35 = 6..2 pounds per gallon. So 15 more gallons(70 - 55) will add 15 X 6.2 = 93 pounds to the 2441 it had with 55 gallons, so the total is 2534 pounds.