Answer:
proportion of students that like either dubstep or trance is 40%
Step-by-step explanation:
Students preferring dubstep : Set [DS] Â = 30%
Students preferring trance music : Set  [TM] = 25%
Students preferring house music : Set [HM] = 20%
Students preferring both dubstep & trance  : Set [DS ⋂ TM] = 15%
Formula : (A U B) = (A) + (B) - (A Â â‹‚ B)
[ DS U TM ] = Â [DS] + [TM] - [DS â‹‚ TM]
= 30% + 25%  - 15% → = 40%