The solid line is described by the equation
... 3x +5y = 10
The shaded portion of the graph is below that line, so you expect something like
... 3x +5y ≤ 10
This matches the 1st and 3rd selections.
The steepest line has an equation like
... 5x +y = 6
The line is dashed and the shading is to the right of it, so you expect something like
... 5x +y > 6.
This matches the 2nd and 3rd selections.
The appropriate selection is the 3rd selection.
