What is the worst-case time complexity of getting the union of two sets (see example code below), if implemented with an array?

Explain your answer (no explanation, no marks) and define your input variables.

def union(self, other):
    res = ArraySet(len(self.array) + len(other.array))
    for i in range(len(self)):
        res.array[i] = self.array[i]
    res.length = self.length
    for j in range(len(other)):
        if other.array[j] not in self:
            res.array[res.length] = other.array[j]
            res.length += 1
    return res