what is the molar concentration of 356.0 mL on and aquaeous H2CO3 solution the required 55.33 mL of 577.0 mM standart solution of NAOH?

Balanced equation for the reaction :
H₂CO₃ + 2NaOH → Na₂CO₃ + 2H₂O
Mole ratio H₂CO₃ : NaOH = 1 : 2

No. of milli-moles of NaOH = (577.0 mmol/L) × (55.33/1000 L) = 31.925 mmol
No. of milli-moles of H₂CO₃ = (31.925 mmol) × (1/2) = 15.963 mmol
Molar concentration of H₂CO₃ = (15.963 mmol) / (356.0 mL) = 0.04484 M