The first thing to do is get all your masses in the same units. You can either convert the mass into kilograms, or your density into grams/metres^3. I'll do the second one.
The conversion rate for kilograms to grams is 10^3g/1kg. This fraction is actually the number 1, because both the top and the bottom are exactly the same. This means you can multiply the density of your object by the fraction, and get the exact same density in a form that will be a lot easier to work with. (Anything times 1 is still what you started with).
(1.98x10^3 kg/m^3) (10^3g/1kg) = (1.98x10^3kg x 10^3g)/(m^3 x kg) (multiply top and bottom of your fractions)
= (1.98x10^6 kg g)/(m^3 kg) (combine powers of ten)
= 1.98x10^6 g/m^3 (cancel kg on top and bottom)
The formula for density is Density = Mass/Volume. Solving for Volume gives Volume = Mass/Density. Inserting your numbers into the equation:
V = (35.4 g)/(1.98x10^6 g/m^3)
V = 35.4/(1.98x10^6 / m^3) (cancel g on top and bottom)
V = 35.4 m^3/1.98x10^6 (multiply top and bottom of fraction by m^3)
V = 1.79x10^-5 m^3 (resolve the fraction)
Remember, you want your answer in cm^3, not m^3. So we need another conversion rate. Knowing that 100 cm/1 m = 1, and that 1^3 = 1, we can say that:
(100 cm/1 m)^3 = 1
100^3 cm^3/m^3 = 1 (cube everything in the brackets)
10^6 cm^3/m^3 = 1
And multiplying your answer by "1" gives you:
(1.79x10^-5 m^3 x 10^6 cm^3)/(m^3) (multiply top and bottom of your fractions)
1.79x10^-5x10^6 cm^3 (cancel m^3 on top and bottom)
17.9 cm^3 (combine powers of ten; simplify)
So your final answer is 17.9 cm^3. Hope this helps!
