Frequency deviation, △f = 75kHz
Highest frequency of modulation,fm = 15kHz
The bandwidth occupied by the spectrum, BW=2nfm where n is the highest order of the significant side-band.
However, approximate expression for spectrum band width is
BW=2(1+mf)fm
=(1+△ffm)fm=2(△f+fm)=2(75+15)=180kHz