The total weight W of such a plane is equal to
W = w + gf
where
w = weight of plane without fuel
g = number of gallons of fuel
f = weight of 1 gallon of fuel.
When carrying g = 10 gallons, the total weight is W = 1955, so
1955 = w + 10f
When carrying g = 42 gallons, the weight is W = 2131, so
2131 = w + 42f
We want to find W when g = 52, and to do this we first need to find the weight of the plane w and the weight of 1 gallon of fuel f.
Solve the system of equations,
w + 10f = 1955
w + 42f = 2131
We can combine the equations like so to eliminate w and solve for f :
(w + 42f) - (w + 10f) = 2131 - 1955
32f = 176
f = 11/2 = 5.5
Then solving for w, we get
w + 10 (5.5) = 1955
w + 55 = 1955
w = 1900
So, when the plane carries g = 52 gallons of fuel, the total weight is
W = 1900 + 52 (5.5) = 2186