0.68x(21.6-8.4÷4) = 0.68x(21.6-2.1) = 0.68x19.5= 0.68x(20-0.5) = 13.6 - 0.34 = 13.26
0.68×(21.6-8.4÷4)=0.68×(21.6-2.1)=0.68×19.5=0.68×20-0.68×0.5=13.6-0.34=13.26