15.58÷8.2-0.72
=(1.9×8.2)÷8.2-0.72
=1.9-0.72
=1.184.5×1.2-3.15÷15
=4.5×(1+0.2)-(15×0.21)÷15
=4.5+0.9-0.21
=5.4-0.21
=5.19