A plane is in level flight at constant speed and each of its two...

Total wing span area, $A = 2 \times 40 = 80{m}^{2}$

Using Bernoulli's equation, we get uplift force as

$A\left({P}_{2} - {P}_{1}\right) = \dfrac{1}{2}ρ\left({V}_{1}^{2} - {V}_{2}^{2}\right)A$

$⇒ mg = \dfrac{1}{2} \times 1\left({70}^{2} - {50}^{2}\right) \times 80$

$⇒ mg = 2400 \times 40$

$⇒ m = 9600kg$