100(x+4)+10x+(x+2)=21[10x+(x+2)]
100x+400+10x+x+2=21[10x+x+2]
100x+10x+x+400+2=210x+21x+42
111x+402=231x+42
231x-111x=402-42
120x=360
x=360÷120
x=3