Taking moments about B gives:
RA × 4 m + 8 kN m + 6 kN × 1 m = 10 kN m
i.e. 4RA = 10 − 8 − 6 = −4
from which, RA =-4/4 = −1 kN
(acting downwards)
Resolving forces vertically gives:
RA + RB + 6 = 0
from which, RB = −RA − 6 = −(−1) − 6
i.e. RB = 1 − 6 = −5 kN
(acting downwards)