Solve using substitution?

Question

x^2 + y^2 = 9; y - x = 3

Answer 1

x² + (3 + x)² = 9
x² + x² + 6x + 9 = 9
2x² + 6x = 0
(2x)(x + 3) = 0
x = 0 , x = - 3
y = 3 , y = 0
Solutions are (0,3) and (- 3,0)

Answer 2

y = 3 + x

x^2 + (x + 3)^2 = 9
x^2 + x^2 + 6x + 9 = 9
2x^2 + 6x = 0
x^2 + 3x = 0
x(x + 3) = 0
x = 0
or
x + 3 = 0 ; x = -3

y = 3 + x
y = 3 ; y = 3 + -3
y = 3 ; y = 0

and then the only solution to fit with y - x = 3 is y = 3 and x = 0
and y = 0, x = -3