How do you solve for mass if KE=0.5mv2

the kilogram (kg), for mass.

the second (s), for time.

the kelvin (K), for temperature.

the ampere (A), for electric current.

the mole (mol), for the amount of a substance.

the candela (cd), for luminous intensity.

the meter (m), for distance.

For geometry we use;

Mile Km Yard, Meter, Foot, inch  cm, mm  = Distance Length/Height/Base

Radius/Radion Circumference Diameter etc.

For weight we use;

Pound,Ounce, Kg, Mgm, Mcgm = Weight

Where; cubic metre (kg/m3) is most usual for density.