Does anyone know how to do this?
c3h5n3o9 contains 100.00g of carbon, calculate the mass of the molecule

I suppose that the question ask the following:

What is the mass of a sample, composed of C₃H₅N₃O₉ molecule, that contains 100 g carbon?

First we calculate the molecular mass of our molecule  C₃H₅N₃O₉.

molecular mass = 12 × 3 + 1 × 5 + 14 × 3 + 16 × 9 = 227 g/mol

Now we devise the following reasoning:

if          227 g of our molecule contains 27 g of carbon

then      X    g of our molecule contains 100 g carbon

X = (100 × 227) / 27 = 840.7 g