Find the position to insert an element into a sorted array

Problem: Find the position to insert an element into a sorted array

A[1] > A[2] > A[3] > ... > A[ n ]

1. Show the best and worst case.
2. Write an algorithm to solve the problem

My answer:

The best case is T(n) = 1 in other words in a first position where n is the size of elements. The worst case will be T(n) = n + 1 in other words the last position + 1.

  def find_position(element, l):
        i = 0
        inserted = False
        for item in l:
            if element < item:
                inserted =  True
                break
            i = i +1
        if not inserted:
            return len(l)
        else:
            return i

Some other students had written a binary search that the worst case is better than mine and told me that my answer is incorrect. But I disagree because the exercise was not explicit to write an optimized algorithm.

Is there any mistake in my logic?

Copyright Notice：Content Author:「Andre Araujo」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/43483367/find-the-position-to-insert-an-element-into-a-sorted-array