\(a.\) \(x\times5,6+x\times3,4+x=123,4\)
\(x\times5,6+x\times3,4+x\times1=123,4\)
\(x\times\left(5,6+3,4+1\right)=123,4\)
\(x\times10=123,4\)
\(x=123,4\div10\)
\(x=12,34\)
b) \(x\div3,1+x\times5+x\div6,7=52,1\)
\(x\div3,1+x\div0,2+x\div6,7=52,1\)
\(x\div\left(3,1+0,2+6,7\right)=52,1\)
\(x\div10=52,1\)
\(x=52,1\times10\)
\(x=521\)