You draw a straight line and then put your number on the line. If you have to find a negative number, you can just go below zero. Positive numbers on a number line are always above zero. Hope this helps!
Formula for slope: 
y₂: 6
y₁: 8
x₂: 1
x₁: -2
Plug them into the slope equation:

--> 
---> 
The slope is
.
Diagram please
Without diagram I cannot tell you the answer
X will equal -7 in this problem