h = 0.1;
Ap = {1.8, 0.7, 0};
Bp = {0.6, h + 0.4, 0};
Cp = {0.6, 0, 0};
Dp = {0, 0.4, 0};
eBA = (Ap - Bp) / (Sqrt[(Ap - Bp).(Ap - Bp)]);
eBD = (Dp - Bp) / (Sqrt[(Dp - Bp).(Dp - Bp)]);
eBC = (Cp - Bp) / (Sqrt[(Cp - Bp).(Cp - Bp)]);
eAC = (Cp - Ap) / (Sqrt[(Cp - Ap).(Cp - Ap)]);
eCD = (Dp - Cp) / (Sqrt[(Dp - Cp).(Dp - Cp)]);
Solve[{TBA eBA + TBC eBC + TBD eBD == 0, -TBA eBA + TAC eAC + {0, -1, 0} == 0, TCD eCD  - TBC eBC  +  {0, 3, 0} - TAC eAC == 0}, {TBA, TBC, TBD, TAC, TCD}]

TBA eBA + TBC eBC + TBD eBD
-TBA eBA + TAC eAC + {0, -1, 0}
TCD eCD  - TBC eBC  +  {0, 3, 0} - TAC eAC