From the situation, we are given that,
a.) Steph has nine (9) mystery books.
b.) The number of mystery books is only 30% of the books that Steph has.
To solve for the total books that Steph have, we generate this equation,
[tex]\text{ Total number of Books = }\frac{No.\text{ of Mystery Books}}{\text{Percetage equivalent of the Mystery Books}}\text{ x 100\%}[/tex]Thus, we get,
[tex]\text{Total number of Books = }\frac{9}{30(\text{\%)}}\text{ x 100(\%)}[/tex][tex]undefined[/tex]