We have,
3y2−5x−3xysum3x2−3y2+4xy−1
⇒3y2−5x−3xy+3x2−3y2+4xy−1
⇒3x2+xy−5x−1
According to given question.
3x2+xy−5x−1−(11x2−2y2−3xy)
=3x2+xy−5x−1−11x2+2y+3xy
=−8x2+4xy−5x+2y−1