A water trough is 10 m long and has a cross-section in the shape of an isosceles trapezoid that is 20 cm wide at the bottom, 60 cm wide at the top, and has height 40 cm. If the trough is being filled with water at the rate of 0.3 m³/min, how fast (in m/min) is the water level rising when the water is 30 cm deep?