8.4x＋3.6x＋3.8＝9.8
8.4x+3.6x=9.8-3.8
12x=6
x=6/12
x=0.5

x÷5＋0.5＝5.5
x÷5＝5.5-0.5
x÷5＝5
x=5*5
x=25