Area of a trapezium = 1/2 × (sum of parallel sides) × height. So area = 1/2 × (31 + 40) × 11 = 390.5 square m. A trapezium has two parallel sides, so first add those two sides, then multiply by the height, and finally take half. The height must be the perpendicular distance between the parallel sides. So the correct choice is 390.5 m².