To find the length of the median of an isosceles trapezoid, we can use the formula:
Median = (Sum of the lengths of the bases) / 2
In this case, the lengths of the bases are 11 and 24. Let's calculate the length of the median:
Median = (11 + 24) / 2
Median = 35 / 2
Median = 17.5 units
Therefore, the length of the median of the isosceles trapezoid is 17.5 units. The correct answer is option c. 17.5 units.