Holly finds that (11m - 13n + 6mn) - (10m - 7n + 3mn) = m - 20n + 9mn. what error did holly make?
she only used the additive inverse of 10m when combining like terms.
she added the polynomials instead of subtracting.
she only used the additive inverses of -7n and 3mn when combining like terms.
she did not combine all like terms.