A sample of ascorbic acid (vitamin C) is synthesized in the laboratory. It contains $1.50 \mathrm{~g}$ of carbon and $2.00 \mathrm{~g}$ of oxygen. Another sample of ascorbic acid isolated from citrus fruits contains $6.35 \mathrm{~g}$ of carbon. According to the law of constant composition, how many grams of oxygen does it contain?