how many milliliters of dry CO2 measured at STP could be evolved in the reaction between 20.0 mL of 0.100 M NaHCO3 and 30.0 mL of 0.0800 M HCl

Answer 1

Write the equation and balance it.
Convert NaHCO3 to moles. moles = M x L = ?
Convert HCl to moles. moles = M x L = ?

Using the coefficients in the balanced equation, convert moles NaHCO3 to moles CO2.
Do the same for moles HCl.
You will obtain two answers; both can't be right, of course. The correct answer in limiting reagent problems is ALWAYS the smaller one and the reagent producing that value is the limiting reagent.
Then take the smaller value and convert to grams. g = moles x molar mass.