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

Are you asking for 6 or 15?