The slope of a line represents the rate of change, that means how many units the graph moves for every unit to the right, in this case for each unit to the right the graph goes 0.75 units down, so the slope must be -0.75.
Lest calculate the slope using 2 points of this graph, (0,1) and (4,-2):
[tex]m=\frac{-2-1}{4-0}=-\frac{3}{4}=-0.75[/tex]
