Which statement describes the heliocentric theory, as stated by Copernicus?

The term heliocentric describes the correct theory, first posed by Nicolas Copernicus, that the Earth is simply one of several planets which orbit the sun.

Explanation:

You can use substitution method
x - y = 7
(x+y)^2=289
So
Since the square of their sum is 298, their sum without being squared is the square root of 289.
Hence,
x - y = 7
x + y = 17
By subtracting you get the following:
= (0) -2(y)=-10
So -2y=-10
y=-10/-2
y=5
Now, plug in y in both equations to get x
x - (5) = 7
x + (5) = 17
Multiply each equation with its opposite y variables
(5) x - (5) = 7
(-5) x + (5) = 17
= 5x -25 = 35
-5x -25 = -85
Now subtract the equations
= 10x + (0) = 120
10x = 120
x = 120/10
x = 12