What is the difference of the values of the two variables in this system of equations?

y = 2x + 1

x + 3y = 10

Y = 2x + 1 ... so sub in 2x + 1 for y in the other equation

x + 3y = 10

x + 3 (2x + 1) = 10

x + 6x + 3 = 10

x + 6x = 10 - 3

7x = 7

x = 1

y = 2x + 1

y = 2 (1) + 1

y = 2 + 1

y = 3

the difference : there can be 2 possible answers for this ...

x - y = 1 - 3 = - 2 OR y - x = 3 - 1 = 2