The simple interest formula for a future quantity is the following:
[tex]A=P(1+rt)[/tex]Where:
[tex]\begin{gathered} P=\text{present value} \\ r=\text{interest rate} \\ t=\text{time} \end{gathered}[/tex]Solving for the present value we get:
[tex]P=\frac{A}{1+rt}[/tex]Replacing the given values:
[tex]P=\frac{86499}{1+(0.1)(5)}[/tex]Solving the operations:
[tex]P=57666[/tex]Therefore, she needs $57666