Hello. can anyone help me with this? i'm not sure how to calculate special relativity formulas.

Object A is a 1000KG

Object B applies 100KG of constant force.

A & B is in a vacuum with no other variables of course.

how fast could object A and B go giving the fact that the mass increases the fast it goes? and how long would it take to get to 25, 50 and 75% it's maximum (or generally close to) speed.

Thank you.