We are given the following rational expression:

For calculation A we notice that when performing an algebraic division the result was:

And the remainder was zero. This means that the numerator can be factored as:

Therefore, calculation A is accurate because it factors the numerator and reveals that the denominator is a factor.
In the case of calculation B we notice that there is an error in the second part of the division. When "2x" was multiplied by the dividend the result is:

But in the operation the result was:

Therefore, Calculation B is inaccurate, because it incorrectly factors the numerator.