Answer :
Since $51 was 3/5 of her money, then if we multiply 3/5 by the amount of money she had, x, we should obtain 51.
[tex]\frac{3}{5}x=51[/tex]We can then solve the above equation for x.
[tex]\begin{gathered} 3\cdot x=51\cdot5 \\ 3\cdot x=255 \\ x=\frac{255}{3} \\ x=85 \end{gathered}[/tex]She had $85.