直接代入即可原式＝3.5+3×4.6＝3.5+13.8＝17.3计算要认真
解：把m=3.5，n=4.6代入得：m+3n=3.5+3×4.6=3.5+13.8=17.3
m＋ 3n＝ 3.5+3×4.6＝3.5+13.8＝17.3
3.5+13.8=17.3
