The drainage area of a town is 12 hectares. Its 40% area is hard pavement (K = 0.85), the 40% area is unpaved streets (K = 0.20) and the remaining is wooded areas (K = 0.15). Assuming the time of concentration for the areas as 30 minutes and using the formula $${{\text{P}}_{\text{s}}} = \frac{{900}}{{{\text{t}} + 60}}$$   the maximum run off is