Answer:
1st box: Asso. prop= m+(4+x)
2nd box: Comm. Prop= m+4=4+m
3rd box: iden. prop= m+0=m
4th box: Zero prop: m x 0=0
Y intercept is negative 8
Because of a linear pair then because of vertical angles and because all angles have to be 180 added up
Plugging in the numbers 7x - 2y = 39 fitted and made sense