What is the solution of the equation -7b=21

Aline that intersects one of two parallel lines intersects the other also always sometimes never

Which is the solution to the inequality? 2 3/52 1/15 b< 3 2/15 b> 3 2/15

Apinhole camera is made out of a light-tight box with a piece of film attached to one side and pinhole on the opposite side. the optimum diameter d(in millimeters) of the pinhole can be modeled by d=1.9[ (5.5 x 10^-4) l) ] ^1/2, where l is the length of the camera box (in millimeters). what is the optimum diameter for a pinhole camera if the camera box has a length of 10 centimeters