Which of these is equivalent to p=2l+2w

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

If there are 3.281 feet in 1 meter, how many inches are in one centimeter

When you find the area of a triangle do you use in. or in2