Three students were given the expression shown (4-9x+21 ) and were asked to take a common factor out of two of the terms. use the drop-down menus to complete the statements about whether each student's answer is an equivalent expression. then choose an expression that is equivalent. chang: 4−3(3x+7) chang's expression is because . benjamin: 4+3(3x+7) benjamin's expression is because . habib: 4+12x habib's expression is because . equivalent expression the correct simplification of this expression is .