1. **State the problem:** We have a catchment area of 1500 m² that received $x$ mm of rainfall in July. The evaporation loss is 15 cm, and the average flow rate at the outlet is 1.71 m³/hr. We need to find the value of $x$ in mm. 2. **Convert evaporation loss to consistent units:** Evaporation loss is 15 cm = 150 mm. 3. **Calculate total volume of flow per month:** Average flow rate = 1.71 m³/hr. Number of hours in July = 31 days × 24 hrs/day = 744 hrs. Total volume of flow = flow rate × time = $1.71 \times 744 = 1271.24$ m³. 4. **Convert volume to mm depth over catchment area:** Volume = area × depth. Depth of runoff = volume / area = $\frac{1271.24}{1500} = 0.8475$ m = 847.5 mm. 5. **Apply water balance equation:** Rainfall depth $x$ (mm) minus evaporation (150 mm) equals runoff depth (847.5 mm): $$x - 150 = 847.5$$ 6. **Solve for $x$:** $$x = 847.5 + 150 = 997.5\text{ mm}$$ **Final answer:** $x = 997.5$ mm of rainfall.