x+y=7
Firstly isolate y :: moving x over with 7 thus y=7-x
Thus you have you answer (7-x) which can be interpreted as x=(7,0) y=(0,7)
With x being negative your slope is -1 one as which x is the representation of 1
x=y+3
subtract 3 from both sides :: resulting in y=x-3
Thus you have you answer (x-3) which can be interpreted as x=(3,0) y=(0,-3)
With x being positive in the situation your slope is positive 1