Please follow the gradual solution:

Part $1)$

Draw the bending moment diagram due to the original loading:

Please indicate the bending moment at $B,M_{B1}=,kN*m$

Part $2)$

Draw the bending moment diagram due to the virtual force $($assume the unit virtual force is to the left$)$:

Please indicate the bending moment at $B,M_{B2}=,kN*m$

Part $3)$

Calculate the horizontal displacement at $B($For the final answer, please take the right as the positive direction$)$:

${}_B=,mm$