you find the answer through the Pythagorean theorem
a^2 + b^2 = c^2 a & b are the legs and c is the hypotenuse
a = 40
b = ?
c = 41
40^2 + b^2 = 41^2
1600 + b^2 = 1681
b^2 = 1681 - 1600
b^2 = 81
b = 9
the length of the other leg is 9
i hope you found this helpful!