In an inverse variation, the function takes the form xy=k
where k is a constant.
Given g(10)=3.5, we find k=xy=3.5*10=35.
This means the function is
m*g(m)=35
When g(m)=5, then m=35/5=7.
Kilogram is an SI unit for mass.
Ounce and pound refer to American system for measuring things, and decakilogram is not the "basic" unit, but kilogram is.