First, let's use the distributive property on 3(a+5)
3(a + 5) = 3a + 3(5) = 3a + 15
Now, let's go back to the inequality
3(a+5) < 9
Use the distributive property
3a + 15 < 9
Subtract both sides by 15
3a < -6
Divide both sides by 3
a < -2
That's your answer.
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