Slope formula
y2-y1/x2-x1
1 = x1
-7 = y1
3 = x2
-21 = y2
Plug in the given values into their corresponding spot in the formula:
-21 - (-7) / 3 - 1
-21 - (-7) is the same as -21 + 7
-21 + 7 is the same as 7 - 21
7 - 21 = -14
3 - 1 = 2
-14/2
-14 divided by 2 = -7
The slope is -7