1. **Problem statement:** We have a right triangle with angles 45°, 45°, and 90°. One leg is 3 cm, and the other leg is $g$. We need to find $g$ in simplest radical form. 2. **Important rule:** In a 45°-45°-90° triangle, the legs are congruent, meaning both legs have the same length. 3. **Formula:** If one leg is $a$, the other leg is also $a$, and the hypotenuse is $a\sqrt{2}$. 4. **Apply the rule:** Since one leg is 3 cm, the other leg $g$ must be equal to 3 cm. 5. **Answer:** $g = 3$ cm. Since the legs are equal, $g = 3$ cm is already in simplest radical form.