解方程．40%x=4.2  ...

①40%x=4.2 0.4x=4.2 0.4x÷0.4=4.2÷0.4 x=10.5②4x-1.6x=36 2.4x=362.4x÷2.4=36÷2.4 x=15 ③2x÷5=152x×5÷5=15×5 2x=75 2x÷2=75÷2 x=37.5