5.8+6.39+3.61
=5.8+(6.39+3.61 )
=5.8+10
=15.8
13.56-1.48-3.52
=13.56-(1.48+3.52)
=13.56-5
=8.56
10.75+( 0.4+2.25 )
=(10.75+2.25)+0.4
=13+0.4
=13.4
1.9+2.07+0.93+1.1
=(1.9+1.1)+(2.07+0.93)
=3+3
=6