Holly finds that open paren 11 m minus 13 n plus 6 m n close paren minus open paren 10 m minus 7 n plus 3 m n close paren is equal to m minus 20 n plus 9 m n What error did Holly make?

The subtraction sign must be distributed to every term in the second parentheses: (11m − 13n + 6mn) − 10m + 7n − 3mn. Holly’s result has m from 11m − 10m, but −20n and 9mn come from combining −13n with −7n and 6mn with +3mn. She changed the sign of 10m but not the signs of the other terms, so the correct choice is “She only used the additive inverse of 10m when combining like terms.”

AI-written and checked against the verified answer.