I have no clue how to do this at all

Zirconium has an hcp crystal structure and a density of 6.51 g/cm3. (a) what is the volume of its unit cell in m3? (b) if the c/a ratio is 1.593, compute the values of c and a.

Two point charges are separated by a certain distance. how does the strength of the electric field produced by the first charge, at the position of the second charge, change if the second charge is doubled? a. the field does not change b. the field strength decreases by half. c. the field strength doubles d. the field strength quadruples

What happens when you slowly pulled the carboard?