How do you find the answer for x + y = 3

What answer:

Maybe graph:

X + Y = 3

X intercept : X+0 = 3

Y intercept : 0 + y = 3

Intercepts are : ( 0,3) , ( 3,0)

Connect them and extend will be the graph.

Y = -x +3 Slope = -1 , Y intercept= 3