Question 452065
*2x-y=12 
to write it in slope-intercept form you have to write it in a way that gives x interms of y meaning(y=...)
so 
2x-y=12,
-y=12-2x
y=2x-12 (slope intercept form)

*for second question
we know that equation of any line is y=mx+b where m is slope and b is y-intercept
and m is given m= -3
so equation of the line is y=-3x+b
and the line passes through point (8,0)
so those coordinates satisfy the equation
then y=-3x+b gives
0=-3(8)+b
so,
0=-24+b 
then b=24
so equation of the line is : y=-3x+24