若单项式a3bn+1和2a2m-1b3是同类项，求3m+n的值
解答: 由题得
解得
当m=2，n=2时，3m+n=3×2+2=6+2=8
两个数的差是105，被减数减少5，减数增加5，它们的差是（ ）
Air pollution has become ______ than ever before. We must do something to stop it.
