Let's tackle subtraction first. Subtraction in hexadecimal works similar to subtraction in decimal. Let's do a pair of decimal problems and see if we can parallel the solution method in hex. Suppose we want to subtract 1586 - 243 (in decimal).
Refraction of Light Rays. the bending or deflection of light rays as they pass through the various media of the eye that include the conjuctiva, cornea, aqueous humor, lens, and vitreous body.
The part of the eye that narrows and widens to control the amount  of light that enters our eye is called the pupil.