Solve 3x = 21.

**The reasoning** To solve **3x = 21**, we need to isolate x (get x alone on one side). Since x is being *multiplied* by 3, we do the opposite operation — we *divide* both sides by 3: 3x ÷ 3 = 21 ÷ 3 x = 7 **Why the wrong options tempt you** - **Option A (6)**: You might subtract 3 from 21 instead of dividing. That's mixing up operations — we divide to undo multiplication, not subtract. - **Option C (8)**: Perhaps you added instead: 21 + 3 = 24, then divided somehow. Wrong approach entirely. - **Option D (9)**: Maybe you divided 21 by something else, or guessed. Always follow the proper steps! **Quick takeaway** To solve equations, do the *opposite* operation: multiplication undoes with division, addition undoes with subtraction — always work to isolate your variable!