Answer:
the Diagonal is 41 units
Explanation:
Since the sides of a rectangle, to be a rectangle, meet at 90° we use Pythagorean Theorem a² + b² = c²
Width and Length are the legs and the diagonal is the hypotenuse
9² + 40² = c²
81 + 1600 = c²
1681 = c²
√1681 = √c²
41 = c