Converting Concentration into Molality

[mary4]

Using the density of 1.022g/mL for seawater, convert the concentrations for the following two ions into molality.


Ion                

Mg²⁺                                          Cl-
  
g/kg

1.284                                    19.353

mM

54.14                                    559.40


I'm really thrown off with what these numbers mean, and the density also confuses me.
Thank you for your help!