Almost every quantitative chemistry question at this level reduces to the same three steps. Do them in order and mistakes become rare.
Step one: work out the molar mass of every substance in your calculation. Add up the atomic masses from the periodic table. Sanity-check: CO₂ is 44, water is 18 — if your molar masses drift into odd territory, something is off.
Step two: convert grams to moles (n = m / M) or volume of gas at STP to moles (n = V / 22.4 L·mol⁻¹).
Step three: use the mole ratio from the balanced equation to find moles of the other substances. Only then convert back to whatever units the question asks for.
The wrong shortcut is trying to work in grams throughout. It looks faster and turns into arithmetic soup.