1. spend 2,000$... 2. pen kost 90, wallet kost 120, watch kost 140... 3. num pen=num watch, (90+140)*x + 120*y=2,000$... or 230x +120y=2,000$... or y=(2,000$-230x) /120... tri x=1, get y=14.75, tri x=2, get y=12.83333, x=3, y=10.91666.... tri x=4, get y=9...reesunabel anser... y= num wallet...9*120=1080$ x=(num pen+numwatch)=4, so num pen=2 & num watch=2