The force applied on the body... help me out

How many molecules are present in 3 mols of silicon dioxide (sio2)?

The focal length of a relaxed human eye is approximately 1.7 cm. when we focus our eyes on a close up object, we can change the refractive power of the eye by about 16 diopters. (a) does the refractive power of our eyes increase or decrease by 16 diopters when we focus closely? explain. (b) calculate the focal length of the eye when we focus closely.

Can anybody me with this? ? (picture included.)