Recall that the product of the slopes of two perpendicular lines is equal to
[tex]-1,[/tex]
therefore, if the slope of the green line is 1/7, and x the slope of the blue line we can set the following equation:
[tex]\frac{1}{7}x=-1.[/tex]
Solving for x we get that:
[tex]x=-7.[/tex]
Answer: Option C.
