\(7^{2x}+7^{2x+3}=344\)
\(7^{2x}+7^{2x}.7^3=344\)
\(7^{2x}+7^{2x}.343=344\)
\(7^{2x}.1+7^{2x}.343=344\)
\(7^{2x}.\left(1+343\right)=344\)
\(7^{2x}.344=344\)
\(7^{2x}=344:344\)
\(7^{2x}=1\)
\(\Rightarrow7^{2x}=7^0\)
\(2x=0\)
\(x=0:2\)
\(x=0\)