The image shows a right triangle with hypotenuse 5 and one leg 3. To find the other leg X, use the Pythagorean theorem: $a^2+b^2=c^2$. Here, $3^2+X^2=5^2$. Solving: $9+X^2=25$, so $X^2=16$ and $X=4$.

Final Answer: $4$