Provide the mass number of fe, which has 29 neutrons

55.845 u

Explanation:

Fe, iron, has 29 neutrons and a atomic mass of 55.845 u

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.

i just calculated it all out, and not including weekends, and all the different days off. as of this school year (2018-2019) students are spending 2198 hours in school this year