Perimeter of the sector?

A normal-level "Length" problem.Forgetting to add the two radii is by far the most common mistake in perimeter problems.

GivenRadius 6 cm / central angle 90° / π = 3.14

Hints

1. The perimeter is the curved arc plus the two straight radii. Start with the arc.
2. The arc is 90/360 of the whole circle.
3. The whole circle is 2 × 6 × 3.14 = 37.68 cm. Taking 90/360 of it, the arc is 9.42 cm.
4. The straight parts are two radii: 6 × 2 = 12 cm.
5. Add the two. 9.42 + 12

Answer 21.42cm

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