24.如【圖24】所示,試求A點及B點反力應爲若干N?(A)RA=4N(t)、RB=16N(t) (B)RA=6N(t)、RB=12N(t) (C)RA=12N(t)、RB=6N(t) (D)RA=16N(t)、RB=4N (t)