Area of parallelogram having a and b as its adjacent sides is 15 sq units. ⇒ |a×b|=15 Area of parallelogram having (3a+2b) and (a+3b) as two adjacent side =|(3a+2b)×(a+3b)| =|3a×a+2b×a+9a×b+6b×b| =|2b×a+9a×b|[∴a×a=b×b=0] =7|a×b|[∴b×a=−a×b] =7×15 =105