[单选题]
In Fig. 4-2, if the tensionvg srrj:wt0;c2 qt:cv 8r7w6p s in the ropek/ y3sq,,pfhf(myz5uk:f bn(0y n( ze s are 50 N, what is the mass of the traffic light?y,k:ynp( nzh/f0 us5m q 3k(zeybf(, f
A. $3.1 \; kg$
B. $4.1 \; kg$
C. $6.1 \; kg$
D. $8.1 \; kg$