Gravitational force is calculated as follows:
F = GMm/R^2, where F is the force of gravity; G is gravitational constant = 6.67408*10^-11 m^3/kg.s^2; M is first mass = 5.3*10^12 kg; m is the second mass = 3.5*10^8 kg; R is the distance between the two masses = 1,800 m.
Substituting;
F = (6.67408*10^-11)*(5.3*10^12)*(3.5*10^8)/1,800^2 = 38,211.17 N ≈ 38.2 kN