The missing blank is 2 because 7+2=9.
Slope-intercept form is y=mx+b
m is slope and b is y-intercept.
So, if you have -5x-3y=3
Make it into y=something
So, -3y=3+5x
y= -3/3 + 5/-3 x
y= -1 - 5/3 x
Same as the first one in your pic.
14 houses does not have street light
20/3~6
20-6=14