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
