1. Write the balanced chemical equation for the reaction
NaOH + HCl → NaCl + H2O

2. Extract the relevant information from the question:
NaOH V = 30 mL , M = 0.10 M
HCl V = 25.0 mL, M = ?

3. Convert milliliters to liters
NaOH V = 0.03 L , M = 0.10 M
HCl V = 0.025 L, M = ?