Answer :

[tex]15f+9>5(5f+3) \\\\ 15f+9>25f+15 \\\\ 15f-25f>15-9 \\\\ -10f>6 \ |:(-2) \\\\ 5f < 3 \\\\ f<\frac{3}{5} \\\\ \boxed{f=(-\infty; \frac{3}{5})}[/tex]
[tex] 15f+9>5(5f+3)\\ 15f+9>25f+15\\ 10f<-6\\ f<-\frac{6}{10}\\ f<-\frac{3}{5}[/tex]

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