If 3x + 5 = 20, find x.

**The reasoning** This is a simple linear equation. We need to isolate x by doing the opposite operations in reverse order: 3x + 5 = 20 First, subtract 5 from both sides: 3x + 5 − 5 = 20 − 5 3x = 15 Then divide both sides by 3: 3x ÷ 3 = 15 ÷ 3 x = 5 The principle here is **inverse operations** — whatever was done to x, we undo it step by step. **Why the wrong options tempt you** - **Option A (3)**: You might pick the coefficient of x by mistake, confusing the number multiplying x with the value of x itself. - **Option C (7)**: This trap catches students who subtract 5 from 20 but forget to divide by 3 — they stop halfway. - **Option D (15)**: You got 3x = 15 correctly but forgot the final step of dividing by 3. **Quick takeaway** Always perform inverse operations in reverse order: undo addition/subtraction first, then undo multiplication/division — and never stop until x stands alone!