SITUATION $4$: For the truss shown below, $P_1=13kN$ and $P_2=6\mathrm{.}5kN.(10$ pts$)$

a$.$ Find the reaction at B in kN $.$

b$.$ If and additional vertical load of $N=27\mathrm{.}5kN$ is applied at $D,$ find the reaction at B in kN $.$

c$.$ If an additional vertical load of $W=27\mathrm{.}5kN$ is applied at $D,$ what will be the axial force in member CD in kN $?$