Answer:
Barbara's did not factor out 63.
Explanation:
63 can be factorize as 63 = 7
9 and 7 d can be factorize as 7 d = 7
d
Therefore common term between 7 d and 63 is 7.
.
In Barbara's equation, it did not factorize 63 as it contains common term 7 in it. Therefore that is the error in Barbara's equation.