Answer:
12 cm
Explanation:
The Pythagorean Theorem is as follows:

A and B represent the side lengths (legs) and C represents the hypotenuse.
The length of one leg equals 5cm. (This can be represented by either a or b)
The hypotenuse equals 13 cm.
Plug these into the equation from above:

Solve for the other leg:
Square what's in the parentheses from above
Subtract 25 from 169
Square root both sides
a = 12 cm
Thus, the length of the other leg is 12 cm.
Let's check our answer:
Square everything
144 + 25 = 169 Add
169 = 169
Because both sides are equal it means that 12 cm is the correct answer.
Hope this helps!!