4 units
1) For this right triangle let's use the Pythagorean Theorem to find that. Note that the hypotenuse is opposite to the right triangle
a² =b² + c²
hypot. ² = leg 1² + leg 2²
2) So we can write
√41 ² = 5² +c²
41 = 25 + c² Let's call c the shortest leg
41-25 = c²
c² = 16
√c=√16
c = 4 -4 does not fit as a measure. So consider only 4 as a valid answer.
3) Hence, the missing leg measures 4 units.