2.1×(3+9.728÷3.2)=2.1×(3+9.728÷4÷4÷0.02)=2.1×(3+2.432÷4÷0.02)=2.1ⅹ(3+0.608÷0.02)=2.1ⅹ(3+3O.4)=2.1ⅹ33.4=(2+0.1)x33.4=66.8+3.34=70.14
2.1x(3+9.728÷3.2)=2.1x(3+3.04)=2.1x6.04=12.684