Choice A is the correct answer. Understanding solution sets means interpreting the inequality's meaning.

1. Solve: Subtract 4: $3x < 15$
2. Complete: Divide by 3: $x < 5$
3. Interpret: ALL values less than 5 (like 4.9, 0, -100, etc.)

?�� Strategic Tip: Solution sets for linear inequalities include infinitely many values, not just integers.

Choice B is incorrect because it reverses the direction to "greater than" instead of "less than". Choice C is incorrect because$x < 5$ uses strict inequality, NOT including 5 itself (that would be $x \leq 5$). Choice D is incorrect because it misunderstands the problem, thinking 4 and 19 are boundaries when they're actually the constants in the inequality.