Tolong dijawab ya please

[tex]f(x) = \frac{5}{6} x + \frac{5}{2} \\ x = \frac{5}{6} y + \frac{5}{2} \\ x = \frac{10y + 30}{12} \\ 12x = 10y + 30 \\ {f}^{ - 1} (x) = \frac{12x - 30}{10} \\ {f}^{ - 1} (a) = \frac{12a - 30}{10} = 9 \\ 12a - 30 = 90 \\ a = \frac{120}{12} = 10[/tex]