Factor polynomials that can be factored as the product of a monomial and a quadratic expression, then further factor the quadratic expression.

Problem

Toby and Bailey were each asked to factor the polynomial expression 7, k, start superscript, 3, end superscript, minus, 28, k, start superscript, 2, end superscript, plus, 21, k. Their responses are shown below.
TobyBailey
7, left parenthesis, k, minus, 1, right parenthesis, left parenthesis, k, minus, 3, right parenthesis7, k, start superscript, 2, end superscript, left parenthesis, k, minus, 1, right parenthesis, left parenthesis, k, minus, 3, right parenthesis
Which student wrote an expression that is equivalent to 7, k, start superscript, 3, end superscript, minus, 28, k, start superscript, 2, end superscript, plus, 21, k ?
Please choose from one of the following options.