Rosa’s work finding the median of a set of test scores is shown below.

Left-brace 80, 70, 90, 80, 90, 65, 100, 100, 90 right-brace

Which statement best describes Rosa’s first error?
She should have reordered the elements from least to greatest.
She should have added the elements and divided by 9.
She should have counted repeated elements only once.
She should have found the difference between the first and last elements.