A flag of height 4 metres is standing on the top of a building. The angle of elevation of the top of the flag from a point X is 45° and the angle of elevation of the top of building from X is 30°. Point X is on the ground level. What is the height (in metres) of the building?

• A. √3 + 2
• B. 2(√3 + 1)
• C. 4(√3 + 1)
• D. (√3 + 1)