A $1\mathrm{.}8-$lb vertical force is applied to the knob of the window$-$opener mechanism shown below

when the crank $BC$ is horizontal. Determine:

a$)$ the moment of the force with respect to point $A,$

b$)$ the moment of the force about the axis $AB,$

c$)$ the perpendicular distance $s$ from the line of action of the force to point $A.$