(4.9+4.9+4.9+4.9)*7.5
=4.9*4*2.5*3
=4.9*3*（4*2.5）
=14.7*10
=147
3.85*1.3+1.5*0.13
=3.85*1.3+0.15*1.3
=（3.85+0.15）*1.3
=4*1.3
=5.2