SOLUTION
Fro m the given information
Let the litres needed bx x
Then the resulting equation is
[tex]18\%x+15\left(43\%\right)=21\%\left(x+15\right)[/tex]This further gives
[tex]0.18x+15\left(0.43\right)=0.21\left(x+15\right)[/tex]Solve the equation for x
[tex]\begin{gathered} 0.18x+6.45=0.21x+3.15 \\ -0.03x=3.15-6.45 \\ x=\frac{-3.3}{-0.03} \\ x=110 \end{gathered}[/tex]Therefore the number of litres needed is 110 litres.
