What's 0.6 written as a fraction in simplest form?

Can someone check if i did this correct. it’s number 4 if you’re wondering.

The measure of one angle of an octagon is two times smaller that of the other seven angles. what is the measure of each angle?

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