F = 6.0 x 10⁻⁸ N
Further explanation
Given
mass of 2 dump trucks = 1500 kg
distance = 50 m
Required
Gravitational force
Solution
Newton's Gravity Law:

with F = gravitational force,
G = gravitational constant,
m1, m2 = mass of object,
r = distance between two objects.
Input the value :
F = (6.67.10⁻¹¹N.m² / kg² x 1500²) : 50²
F = 6.0 x 10⁻⁸ N