Answer
200 N, 600 N
Work Step by Step
If the second force points due east, both forces point in the same direction and the magnitude of resultant force will be:
$F_{1}+F_{2}=F_{R}$
So:
$F_{2}=F_{R}-F_{1}=400 N-200N=200N$
If the second force points due west, both forces point in the opposite direction and the magnitude of resultant force will be:
$F_{2}-F_{1}=F_{R}$
So,
$F_{2}=F_{R}+F_{1}=400 N+200N=600N$
