Answer
The solution set is $[\displaystyle \frac{20}{3}, \infty)$
Work Step by Step
The idea is to isolate x on one side.
Adding, subtracting or multiplying/dividing with a positive number preserves order (the inequality symbol remains).
Multiplying/dividing with a negative number inverts the order (the inequality symbol changes)
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$ 3x-7 \geq 13\qquad $ ... $/+7$
$ 3x \geq 20 \qquad $ ... $/\div 3$, (positive)
$ x \displaystyle \geq \frac{20}{3}$
The solution set is $[\displaystyle \frac{20}{3}, \infty)$
