Assuming, as usual, that the composition of the unknown compound is given in mass percentages, since we know that we have 2.880 g of this compound, we can apply each percentage to get the mass we will get of each element.
For carbon, we have 66.05%, so:
[tex]m_C=0.6605\cdot2.880g=1.90224g\approx1.902g[/tex]
For oxygen, we have 23.18%, so:
[tex]m_O=0.2318\cdot2.880g=0.667584g\approx0.6676g[/tex]
For hydrogen, we have 6.72%, so:
[tex]m_H=0.0672\cdot2.880g=0.193536g\approx0.1935g[/tex]
For nitrogen, we have 4.05%, so:
[tex]m_N=0.0405\cdot2.880g=0.11664g\approx0.1166g[/tex]
