determine the minimum weight at which the tube wont tip over

https://kek.gg/i/kpfvV.jpg

r1=r2=120mm or 0.12m

D=400mm=0.40m

G=200N

What I managed to get :

r3=r1+r2=0.24m

length between AB=D-r3=0.16m

cosα=r3/(r1+r2)=2/3

cosα^-1=48.19

sinα=sin(48.19)=0.75

right force = left force

bottom reaction = G = 200N

.∑Fx=0 F[AB]cos(48.19) - F[D]=0

F[D]=F[AB]cos(48.19) = 179N

.∑Fy=0 F[AB]sin(48.19) - F[G]=0

F[AB]sin(48.19) = 200

F[AB]=268N

∑M=? W=? I dont know how to set up the momentum