Answer: The answer is 18 units.
Step-by-step explanation: We are given a trapezoid KLMJ with pair of parallel sides KL and MJ. Also, KJ = 16 units, MJ = 40 units, JL = 18 units and ∠JLM = 45°.
Therefore, ∠KLM = 180° - 45° = 135°.
We have drawn KM as shown in the attached figure.
Now, since the given figure is an isosceles trapezoid, and we know that the diagonals of an isosceles trapezoid are congruent, so we must have
JL = KM.
Since JL = 18 units, so KM = 18 units.
Thus, the answer is 18 units.