The slope can be worked out by the equation:
[tex]\frac{(y2 - y1) }{(x2-x1)}[/tex]
So with the coordinates (1,2) and (-2,4):
x1 = 1 y1= 2 and x2 = -2 y2 =4
Note that x1 and y1 use the same coordinate, vice versa with x2 and y2.
Tip: The equation can be y1-y2 and x1-y2 too (have a think why)
[tex]\frac{(y2 - y1) }{(x2-x1)}[/tex]
[tex]\frac{(4 - 2) }{(-2-1)}[/tex]
[tex]\frac{(2) }{(-3)}[/tex]
So the answer is 2/-3, which is the same as C) -2/3