To determine the weight of the plane with 81 gallons of fuel, the first step is to determine the equation of the line:
We know that the slope of the line is m=5.5 and an ordered pair (52,2386)
Using the slope-intercept form, the first step is to replace the slope in the expression:

Next, replace the x and y values of the known ordered pair, this way, the y-intercept will be the only unknown term of the equation:

Subtract 286 from both sides of the equal sign to calculate the value of b:

Now we know that the y-intercept is b=2100pounds (this is the weight of the plane when its tanks are empty)
The equation of the line is:

Now we can determine the weight of the place with x=81 gallons of fuel:

With 81 gallons of fuel, the weight of the plane will be 2545.5 pounds