Answer:
[tex]\boxed {f < 4}[/tex]
Step-by-step explanation:
Solve the following inequality:
[tex]3f + 9 < 21[/tex]
-Subtract [tex]9[/tex] on both sides:
[tex]3f + 9 - 9 < 21 - 9[/tex]
[tex]3f < 12[/tex]
-Divide both sides by [tex]3[/tex]:
[tex]\frac{3f}{3} < \frac{12}{3}[/tex]
[tex]\boxed {f < 4}[/tex]