Áp dụng t/c dãy tỉ số bằng nhau .
\(\frac{1+2y}{18}=\frac{1 +6y}{6x}=\frac{1+2y+1+6y}{18+6x}=\frac{2+8y}{18+6x}=\frac{2\left(1+4y\right)}{2\left(9+3x\right)}=\frac{1+4y}{9+3x}\)
Vì \(\frac{1+4y}{18}=\frac{1+4y}{9+3x}\Rightarrow18=9+3x\Rightarrow3x=9\Rightarrow x=3\)
Vậy x=3