Slope form is y/x
to find this subtract -5, 7 by -3, 5 to get
-2, 2 and putting it in slope format....2/-2 which would be -1 or just -x (means -1x)
so far we've found out.....y = -x (+b)
b is what we need to find now so... plug in one of the coordinates
7=5+b (5 because --5 is positive 5)
b=2
so FINALLY the equation would be y = -x + 2
Ten percent of 640 is 64.
640/100=6.4
6.4*10=64.
There are many other ways to find this but that is the way I have always used :)
Hope this helps!
Do you mean "perpendicular to k"? We have no line c there so I'm going with line k. First we need the slope of line k. Fitting those values into the slope formula we have

. So the slope of k is 9. The slope of a line perpendicular to k has the opposite sign and the fraction is flipped. The perpendicular slope then is -1/9.
If there are ten black pens, eight blue pens, and twenty pens in total, then there are 2 red pens. This means that the ratio of red to black is 2:10=1:5. Hope this helps!