Choice Dhoice C is the correct answer.

1. Start with the equation: $7x - 21 = 14$
2. Add 21 to both sides: $7x = 14 + 21$
3. Simplify: $7x = 35$
4. Divide both sides by 7: $x = \frac{35}{7}$
5. Simplify: $x = 5$
6. Verify: $7(5) - 21 = 35 - 21 = 14$ ✓

Choice Dhoice B is incorrect because this results from subtracting 21 from 14: $-7$, then $-7/7 = -1$. We must add to undo subtraction.

Choice Dhoice D is incorrect because this is the value of $7x$. Don't stop early!

Choice Dhoice A is incorrect because this results from multiplying 35 by 7: $245$.