Q.Write the set $\{7, 14, 21, 28, 35\}$ in set-builder form.

Look for the shared arithmetic pattern among the listed numbers and state it as a rule.

All five numbers are multiples of 7, stopping at 35.

Step 1 — Study the elements. $7, 14, 21, 28, 35$ are $7\times1, 7\times2, 7\times3, 7\times4, 7\times5$ — each a multiple of 7.

Step 2 — Find the bound. The largest is 35; the next multiple, 42, is excluded, so $x \le 35$.

Step 3 — Write and verify the rule. Testing multiples of 7 up to 35 gives exactly the five listed numbers.

Stating the rule as "$x$ is divisible by 7" without an upper bound would wrongly include 42, 49, and every larger multiple of 7 as well.