Please use the Line wizard titled "Perpendicular line passing through a point". Since y=6 if x=0, use the point (0,6).

Please use one of the following links to obtain a free trial of the program:

Windows: https://www.softmath.com/tr/alg51win-tr-en.exe

Mac: https://www.softmath.com/tr/alg51mac-tr-en.dmg