[tex]\begin{gathered} \text{Total interest= \$330} \\ Total\text{ invested}=\text{ \$6,400} \\ \text{For account 1} \\ i=\text{ 4\%=0.04} \\ \text{amount invested =x} \\ Hence \\ \text{Interest 1= (x)(0.04)(1)} \\ \text{For account 2} \\ i=\text{ 6\%=0.0}6 \\ \text{amount invested =6,400-x} \\ \text{Hence} \\ \text{Interest 2= (6,400-x)(0.06)(1)} \\ However \\ \text{Interest 1}+\text{Interest }2=\text{Total interest} \\ \text{(x)(0.04)(1)+(6,400-x)(0.06)(1)}=330 \\ The\text{ equation model is (x)(0.04)(1)+(6,400-x)(0.06)(1)}=330 \end{gathered}[/tex]