A stone is dropped from the top of a building. When it crosses a point $5 \mathrm{m}$ below the top, another stone starts to fall from a point $25 \mathrm{m}$ below the top. Both stones reach the bottom of building simultaneously. The height of the building is :

• A

  $25 \mathrm{m}$
• Correct answer
  B

  $45 \mathrm{m}$
• C

  $35 \mathrm{m}$
• D

  $50 \mathrm{m}$

Hence, the correct answer is option: 'B'.