Simply multiply the known quantities with conversion factors given in the table to convert units.
2.54 cm = 1 inch (from a conversion table)
Then, a length 1 ft = 12 inches
= 12 X 2.54 cm
= 30.48 cm
Also, 1 lb = 450 gms (approx) (from conversion table)
Thus, 2.2 lb = 990 gms (approx)
This, way one should proceed in converting units.