Since it is a right triangle, you can use the Pythagorean theorem to solve it.
The Pythagorean theorem says that the sum of the squares of the legs of the triangle is equal to the sqauare of the hypotenuse.
ac^2 + ba^2 = cb^2
ac^2 + 5^2 = 13^2
ac^2 + 25 = 169 (simplify the squares)
ac^2 = 144 (subtract 25 from both sides)
ac = 12 (take the square root of both sides)
The correct answer is C. 12 cm.
hope this helps =)
