Based from Newton's second law of motion, the net force exerted on an object is equal to the product of its mass and the acceleration.
F = m x a
From this item, we are given of the expulsion rate and the speed, which may also be multiplied with each other in order to determine the net force.
F = (1400 kg/s)(3.6 x 10^4 m/s)
Simplifying,
F = 50400000 N
In scientific notation,
F = 5.04 x 10^7 N