Question 1112356
{{{ -4y + 7 = 11 }}}
{{{ -4y = 4 }}}
{{{ y = -1 }}}
--------------------
No matter where you move along this
line, {{{ y }}} never changes. It is
always {{{ -1 }}}. 
( 3, -1 ) and ( 12,706, -1 ) are both
points on this line.
----------------------------
The only way this can happen is if
the line is horizontal, so the slope
is [ change in y ] / [ change in x ] and
[ change in y ] is always {{{ 0 }}},
so slope = {{{ 0 }}}