What is the area of an isosceles trapezoid if the length of its shorter base is 18 cm, the length of an altitude is 9 cm, and the measure of the acute angle is 45º.

Check the picture below.

since we know the acute angle is 45°, that angle with the bottom base and the slanted line and the altitude make a 45-45-90 triangle, and thus we can get the value of that section at the bottom, as you see in the picture, thus the longer base is 9 + 18 + 9, or 36.

The correct answer would be the fourth choice