If $\frac{21x-6}{4}-9\le0$ and $\frac{x-1}{3}+1\ge0, x\in\mathbb{R}$ then $x$ lies in the interval
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Logic Tip: Always express compound inequalities on a mental (or sketched) number line. "Less than or equal to" points left, and "greater than or equal to" points right. The region where the two lines overlap is your final answer.