The mass is given to 3 significant figures, so we need a value for the acceleration due to gravity that is at least 3 significant figures. The standard value is 9.80665 m/s². Using that, the force is ...
... F = ma = (635 kg)(9.80665 m/s²) = 6227.22275 N
Since the mass is only good to 3 significant figures, the force must be rounded to that precision: 6230 N.
