Question 207179
slope is rise over run, that is, (change in y) / (change in x)
In this case change in y doesn't have to be 4 and change in x doesn't have to be 5, just the ratio or fraction has to be the same.
 
In this case, going from the second point to the first (doesn't matter whether 1st to 2nd or 2nd to 1st, BUT it has to be the same direction for both x and y), rise over run is:
{{{(8-4)/(-2 - x)=4/5)}}}  simplifying 8-4
{{{4/(-2 - x)=4/5}}}   dividing both sides by 4 (makes equation less complicated and the numbers smaller)
{{{1/(-2 - x)=1/5}}}   cross multiplying or, equivalently, multiplying both sides by 5 and (-2-x)) 
{{{5=-2 - x}}}   adding 2 to both sides
{{{7 = -x}}}   multiplying both sides by -1
{{{x = -7}}}