sound physics question?

You are sitting in L132 trying to write a Chemistry mid-term. Being the boy-scout type (i.e. being prepared) you bring along a sound level meter in case you have to register a complaint about the noise level while you are writing. It is reading a tolerable 50.0 dB. However, someone starts to work on the roof, raising the sound level to a reading of 75.0 dB. By what factor has the sound intensity increased?