Explanation:

- Base of the isosceles triangle: 10 cm.

- Altitude (height) of the triangle: 12 cm from the base to the apex.

- Isosceles triangle: Two sides are equal, with the altitude creating two right triangles.

- For each right triangle:

- Half the base = 5 cm (as the altitude bisects the base).

- Use Pythagorean theorem: \( c = \sqrt{(5)^2 + (12)^2} \).

- Calculation: \( c = \sqrt{25 + 144} = \sqrt{169} = 13 \) cm.

- Therefore, the length of each equal side is 13 cm.

Correct Answer: 13 cm