Titration calculations

A student titrates 25.0 cm³ of hydrochloric acid with 0.200 mol/dm³ sodium hydroxide solution. The average volume of NaOH used to reach the end‑point is 18.0 cm³. Assuming the reaction is $\text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O}$, what is the concentration of the hydrochloric acid?