The pressure on the top surface of an aeroplane wing was $0.\text{9}0\times \text{1}{0}^{\text{5}}\text{Pa}$  and at the bottom surface is $0.\text{91}\times \text{1}{0}^{\text{5}}\text{Pa}$ . If the area of each surface is $\text{4}0{\text{m}}^{\text{2}},$  the net lift force on the wing is