You do not state an initial velocity, so let's assume it is 0.
vf = vo + at vo = original velocity = 0
vf = at a is in seconds 75m/s^2 t is in weeks and one or the other has to match
convert weeks to seconds 3600 sec/hr x 24 hr/day x 21 day = t
multiply this by a to find the final velocity (divide by 1000 m/km to get km/sec)
Then for the distance , starting at xo = 0
xf = xo + vot + 1/2 a t^2 vo and xo = 0 make sure a and t are in the same time units..... Done !